Lib/test/test_io.py

"""Unit tests for the io module."""

# Tests of io are scattered over the test suite:
# * test_bufio - tests file buffering
# * test_memoryio - tests BytesIO and StringIO
# * test_fileio - tests FileIO
# * test_file - tests the file interface
# * test_io - tests everything else in the io module
# * test_univnewlines - tests universal newline support
# * test_largefile - tests operations on a file greater than 2**32 bytes
#     (only enabled with -ulargefile)

################################################################################
# ATTENTION TEST WRITERS!!!
################################################################################
# When writing tests for io, it's important to test both the C and Python
# implementations. This is usually done by writing a base test that refers to
# the type it is testing as a attribute. Then it provides custom subclasses to
# test both implementations. This file has lots of examples.
################################################################################

from __future__ import print_function
from __future__ import unicode_literals

import os
import sys
import time
import array
import random
import unittest
import weakref
import warnings
import abc
import signal
import errno
from itertools import cycle, count
from collections import deque
from UserList import UserList
from test import test_support as support
import contextlib

import codecs
import io  # C implementation of io
import _pyio as pyio # Python implementation of io
try:
    import threading
except ImportError:
    threading = None
try:
    import fcntl
except ImportError:
    fcntl = None

__metaclass__ = type
bytes = support.py3k_bytes

def _default_chunk_size():
    """Get the default TextIOWrapper chunk size"""
    with io.open(__file__, "r", encoding="latin1") as f:
        return f._CHUNK_SIZE


class MockRawIOWithoutRead:
    """A RawIO implementation without read(), so as to exercise the default
    RawIO.read() which calls readinto()."""

    def __init__(self, read_stack=()):
        self._read_stack = list(read_stack)
        self._write_stack = []
        self._reads = 0
        self._extraneous_reads = 0

    def write(self, b):
        self._write_stack.append(bytes(b))
        return len(b)

    def writable(self):
        return True

    def fileno(self):
        return 42

    def readable(self):
        return True

    def seekable(self):
        return True

    def seek(self, pos, whence):
        return 0   # wrong but we gotta return something

    def tell(self):
        return 0   # same comment as above

    def readinto(self, buf):
        self._reads += 1
        max_len = len(buf)
        try:
            data = self._read_stack[0]
        except IndexError:
            self._extraneous_reads += 1
            return 0
        if data is None:
            del self._read_stack[0]
            return None
        n = len(data)
        if len(data) <= max_len:
            del self._read_stack[0]
            buf[:n] = data
            return n
        else:
            buf[:] = data[:max_len]
            self._read_stack[0] = data[max_len:]
            return max_len

    def truncate(self, pos=None):
        return pos

class CMockRawIOWithoutRead(MockRawIOWithoutRead, io.RawIOBase):
    pass

class PyMockRawIOWithoutRead(MockRawIOWithoutRead, pyio.RawIOBase):
    pass


class MockRawIO(MockRawIOWithoutRead):

    def read(self, n=None):
        self._reads += 1
        try:
            return self._read_stack.pop(0)
        except:
            self._extraneous_reads += 1
            return b""

class CMockRawIO(MockRawIO, io.RawIOBase):
    pass

class PyMockRawIO(MockRawIO, pyio.RawIOBase):
    pass


class MisbehavedRawIO(MockRawIO):
    def write(self, b):
        return MockRawIO.write(self, b) * 2

    def read(self, n=None):
        return MockRawIO.read(self, n) * 2

    def seek(self, pos, whence):
        return -123

    def tell(self):
        return -456

    def readinto(self, buf):
        MockRawIO.readinto(self, buf)
        return len(buf) * 5

class CMisbehavedRawIO(MisbehavedRawIO, io.RawIOBase):
    pass

class PyMisbehavedRawIO(MisbehavedRawIO, pyio.RawIOBase):
    pass


class CloseFailureIO(MockRawIO):
    closed = 0

    def close(self):
        if not self.closed:
            self.closed = 1
            raise IOError

class CCloseFailureIO(CloseFailureIO, io.RawIOBase):
    pass

class PyCloseFailureIO(CloseFailureIO, pyio.RawIOBase):
    pass


class MockFileIO:

    def __init__(self, data):
        self.read_history = []
        super(MockFileIO, self).__init__(data)

    def read(self, n=None):
        res = super(MockFileIO, self).read(n)
        self.read_history.append(None if res is None else len(res))
        return res

    def readinto(self, b):
        res = super(MockFileIO, self).readinto(b)
        self.read_history.append(res)
        return res

class CMockFileIO(MockFileIO, io.BytesIO):
    pass

class PyMockFileIO(MockFileIO, pyio.BytesIO):
    pass


class MockNonBlockWriterIO:

    def __init__(self):
        self._write_stack = []
        self._blocker_char = None

    def pop_written(self):
        s = b"".join(self._write_stack)
        self._write_stack[:] = []
        return s

    def block_on(self, char):
        """Block when a given char is encountered."""
        self._blocker_char = char

    def readable(self):
        return True

    def seekable(self):
        return True

    def writable(self):
        return True

    def write(self, b):
        b = bytes(b)
        n = -1
        if self._blocker_char:
            try:
                n = b.index(self._blocker_char)
            except ValueError:
                pass
            else:
                if n > 0:
                    # write data up to the first blocker
                    self._write_stack.append(b[:n])
                    return n
                else:
                    # cancel blocker and indicate would block
                    self._blocker_char = None
                    return None
        self._write_stack.append(b)
        return len(b)

class CMockNonBlockWriterIO(MockNonBlockWriterIO, io.RawIOBase):
    BlockingIOError = io.BlockingIOError

class PyMockNonBlockWriterIO(MockNonBlockWriterIO, pyio.RawIOBase):
    BlockingIOError = pyio.BlockingIOError


class IOTest(unittest.TestCase):

    def setUp(self):
        support.unlink(support.TESTFN)

    def tearDown(self):
        support.unlink(support.TESTFN)

    def write_ops(self, f):
        self.assertEqual(f.write(b"blah."), 5)
        f.truncate(0)
        self.assertEqual(f.tell(), 5)
        f.seek(0)

        self.assertEqual(f.write(b"blah."), 5)
        self.assertEqual(f.seek(0), 0)
        self.assertEqual(f.write(b"Hello."), 6)
        self.assertEqual(f.tell(), 6)
        self.assertEqual(f.seek(-1, 1), 5)
        self.assertEqual(f.tell(), 5)
        self.assertEqual(f.write(bytearray(b" world\n\n\n")), 9)
        self.assertEqual(f.seek(0), 0)
        self.assertEqual(f.write(b"h"), 1)
        self.assertEqual(f.seek(-1, 2), 13)
        self.assertEqual(f.tell(), 13)

        self.assertEqual(f.truncate(12), 12)
        self.assertEqual(f.tell(), 13)
        self.assertRaises(TypeError, f.seek, 0.0)

    def read_ops(self, f, buffered=False):
        data = f.read(5)
        self.assertEqual(data, b"hello")
        data = bytearray(data)
        self.assertEqual(f.readinto(data), 5)
        self.assertEqual(data, b" worl")
        self.assertEqual(f.readinto(data), 2)
        self.assertEqual(len(data), 5)
        self.assertEqual(data[:2], b"d\n")
        self.assertEqual(f.seek(0), 0)
        self.assertEqual(f.read(20), b"hello world\n")
        self.assertEqual(f.read(1), b"")
        self.assertEqual(f.readinto(bytearray(b"x")), 0)
        self.assertEqual(f.seek(-6, 2), 6)
        self.assertEqual(f.read(5), b"world")
        self.assertEqual(f.read(0), b"")
        self.assertEqual(f.readinto(bytearray()), 0)
        self.assertEqual(f.seek(-6, 1), 5)
        self.assertEqual(f.read(5), b" worl")
        self.assertEqual(f.tell(), 10)
        self.assertRaises(TypeError, f.seek, 0.0)
        if buffered:
            f.seek(0)
            self.assertEqual(f.read(), b"hello world\n")
            f.seek(6)
            self.assertEqual(f.read(), b"world\n")
            self.assertEqual(f.read(), b"")

    LARGE = 2**31

    def large_file_ops(self, f):
        assert f.readable()
        assert f.writable()
        self.assertEqual(f.seek(self.LARGE), self.LARGE)
        self.assertEqual(f.tell(), self.LARGE)
        self.assertEqual(f.write(b"xxx"), 3)
        self.assertEqual(f.tell(), self.LARGE + 3)
        self.assertEqual(f.seek(-1, 1), self.LARGE + 2)
        self.assertEqual(f.truncate(), self.LARGE + 2)
        self.assertEqual(f.tell(), self.LARGE + 2)
        self.assertEqual(f.seek(0, 2), self.LARGE + 2)
        self.assertEqual(f.truncate(self.LARGE + 1), self.LARGE + 1)
        self.assertEqual(f.tell(), self.LARGE + 2)
        self.assertEqual(f.seek(0, 2), self.LARGE + 1)
        self.assertEqual(f.seek(-1, 2), self.LARGE)
        self.assertEqual(f.read(2), b"x")

    def test_invalid_operations(self):
        # Try writing on a file opened in read mode and vice-versa.
        for mode in ("w", "wb"):
            with self.open(support.TESTFN, mode) as fp:
                self.assertRaises(IOError, fp.read)
                self.assertRaises(IOError, fp.readline)
        with self.open(support.TESTFN, "rb") as fp:
            self.assertRaises(IOError, fp.write, b"blah")
            self.assertRaises(IOError, fp.writelines, [b"blah\n"])
        with self.open(support.TESTFN, "r") as fp:
            self.assertRaises(IOError, fp.write, "blah")
            self.assertRaises(IOError, fp.writelines, ["blah\n"])

    def test_raw_file_io(self):
        with self.open(support.TESTFN, "wb", buffering=0) as f:
            self.assertEqual(f.readable(), False)
            self.assertEqual(f.writable(), True)
            self.assertEqual(f.seekable(), True)
            self.write_ops(f)
        with self.open(support.TESTFN, "rb", buffering=0) as f:
            self.assertEqual(f.readable(), True)
            self.assertEqual(f.writable(), False)
            self.assertEqual(f.seekable(), True)
            self.read_ops(f)

    def test_buffered_file_io(self):
        with self.open(support.TESTFN, "wb") as f:
            self.assertEqual(f.readable(), False)
            self.assertEqual(f.writable(), True)
            self.assertEqual(f.seekable(), True)
            self.write_ops(f)
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.readable(), True)
            self.assertEqual(f.writable(), False)
            self.assertEqual(f.seekable(), True)
            self.read_ops(f, True)

    def test_readline(self):
        with self.open(support.TESTFN, "wb") as f:
            f.write(b"abc\ndef\nxyzzy\nfoo\x00bar\nanother line")
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.readline(), b"abc\n")
            self.assertEqual(f.readline(10), b"def\n")
            self.assertEqual(f.readline(2), b"xy")
            self.assertEqual(f.readline(4), b"zzy\n")
            self.assertEqual(f.readline(), b"foo\x00bar\n")
            self.assertEqual(f.readline(None), b"another line")
            self.assertRaises(TypeError, f.readline, 5.3)
        with self.open(support.TESTFN, "r") as f:
            self.assertRaises(TypeError, f.readline, 5.3)

    def test_raw_bytes_io(self):
        f = self.BytesIO()
        self.write_ops(f)
        data = f.getvalue()
        self.assertEqual(data, b"hello world\n")
        f = self.BytesIO(data)
        self.read_ops(f, True)

    def test_large_file_ops(self):
        # On Windows and Mac OSX this test comsumes large resources; It takes
        # a long time to build the >2GB file and takes >2GB of disk space
        # therefore the resource must be enabled to run this test.
        if sys.platform[:3] == 'win' or sys.platform == 'darwin':
            support.requires(
                'largefile',
                'test requires %s bytes and a long time to run' % self.LARGE)
        with self.open(support.TESTFN, "w+b", 0) as f:
            self.large_file_ops(f)
        with self.open(support.TESTFN, "w+b") as f:
            self.large_file_ops(f)

    def test_with_open(self):
        for bufsize in (0, 1, 100):
            f = None
            with self.open(support.TESTFN, "wb", bufsize) as f:
                f.write(b"xxx")
            self.assertEqual(f.closed, True)
            f = None
            try:
                with self.open(support.TESTFN, "wb", bufsize) as f:
                    1 // 0
            except ZeroDivisionError:
                self.assertEqual(f.closed, True)
            else:
                self.fail("1 // 0 didn't raise an exception")

    # issue 5008
    def test_append_mode_tell(self):
        with self.open(support.TESTFN, "wb") as f:
            f.write(b"xxx")
        with self.open(support.TESTFN, "ab", buffering=0) as f:
            self.assertEqual(f.tell(), 3)
        with self.open(support.TESTFN, "ab") as f:
            self.assertEqual(f.tell(), 3)
        with self.open(support.TESTFN, "a") as f:
            self.assertTrue(f.tell() > 0)

    def test_destructor(self):
        record = []
        class MyFileIO(self.FileIO):
            def __del__(self):
                record.append(1)
                try:
                    f = super(MyFileIO, self).__del__
                except AttributeError:
                    pass
                else:
                    f()
            def close(self):
                record.append(2)
                super(MyFileIO, self).close()
            def flush(self):
                record.append(3)
                super(MyFileIO, self).flush()
        f = MyFileIO(support.TESTFN, "wb")
        f.write(b"xxx")
        del f
        support.gc_collect()
        self.assertEqual(record, [1, 2, 3])
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.read(), b"xxx")

    def _check_base_destructor(self, base):
        record = []
        class MyIO(base):
            def __init__(self):
                # This exercises the availability of attributes on object
                # destruction.
                # (in the C version, close() is called by the tp_dealloc
                # function, not by __del__)
                self.on_del = 1
                self.on_close = 2
                self.on_flush = 3
            def __del__(self):
                record.append(self.on_del)
                try:
                    f = super(MyIO, self).__del__
                except AttributeError:
                    pass
                else:
                    f()
            def close(self):
                record.append(self.on_close)
                super(MyIO, self).close()
            def flush(self):
                record.append(self.on_flush)
                super(MyIO, self).flush()
        f = MyIO()
        del f
        support.gc_collect()
        self.assertEqual(record, [1, 2, 3])

    def test_IOBase_destructor(self):
        self._check_base_destructor(self.IOBase)

    def test_RawIOBase_destructor(self):
        self._check_base_destructor(self.RawIOBase)

    def test_BufferedIOBase_destructor(self):
        self._check_base_destructor(self.BufferedIOBase)

    def test_TextIOBase_destructor(self):
        self._check_base_destructor(self.TextIOBase)

    def test_close_flushes(self):
        with self.open(support.TESTFN, "wb") as f:
            f.write(b"xxx")
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.read(), b"xxx")

    def test_array_writes(self):
        a = array.array(b'i', range(10))
        n = len(a.tostring())
        with self.open(support.TESTFN, "wb", 0) as f:
            self.assertEqual(f.write(a), n)
        with self.open(support.TESTFN, "wb") as f:
            self.assertEqual(f.write(a), n)

    def test_closefd(self):
        self.assertRaises(ValueError, self.open, support.TESTFN, 'w',
                          closefd=False)

    def test_read_closed(self):
        with self.open(support.TESTFN, "w") as f:
            f.write("egg\n")
        with self.open(support.TESTFN, "r") as f:
            file = self.open(f.fileno(), "r", closefd=False)
            self.assertEqual(file.read(), "egg\n")
            file.seek(0)
            file.close()
            self.assertRaises(ValueError, file.read)

    def test_no_closefd_with_filename(self):
        # can't use closefd in combination with a file name
        self.assertRaises(ValueError, self.open, support.TESTFN, "r", closefd=False)

    def test_closefd_attr(self):
        with self.open(support.TESTFN, "wb") as f:
            f.write(b"egg\n")
        with self.open(support.TESTFN, "r") as f:
            self.assertEqual(f.buffer.raw.closefd, True)
            file = self.open(f.fileno(), "r", closefd=False)
            self.assertEqual(file.buffer.raw.closefd, False)

    def test_garbage_collection(self):
        # FileIO objects are collected, and collecting them flushes
        # all data to disk.
        f = self.FileIO(support.TESTFN, "wb")
        f.write(b"abcxxx")
        f.f = f
        wr = weakref.ref(f)
        del f
        support.gc_collect()
        self.assertTrue(wr() is None, wr)
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.read(), b"abcxxx")

    def test_unbounded_file(self):
        # Issue #1174606: reading from an unbounded stream such as /dev/zero.
        zero = "/dev/zero"
        if not os.path.exists(zero):
            self.skipTest("{0} does not exist".format(zero))
        if sys.maxsize > 0x7FFFFFFF:
            self.skipTest("test can only run in a 32-bit address space")
        if support.real_max_memuse < support._2G:
            self.skipTest("test requires at least 2GB of memory")
        with self.open(zero, "rb", buffering=0) as f:
            self.assertRaises(OverflowError, f.read)
        with self.open(zero, "rb") as f:
            self.assertRaises(OverflowError, f.read)
        with self.open(zero, "r") as f:
            self.assertRaises(OverflowError, f.read)

    def test_flush_error_on_close(self):
        f = self.open(support.TESTFN, "wb", buffering=0)
        def bad_flush():
            raise IOError()
        f.flush = bad_flush
        self.assertRaises(IOError, f.close) # exception not swallowed
        self.assertTrue(f.closed)

    def test_multi_close(self):
        f = self.open(support.TESTFN, "wb", buffering=0)
        f.close()
        f.close()
        f.close()
        self.assertRaises(ValueError, f.flush)

    def test_RawIOBase_read(self):
        # Exercise the default RawIOBase.read() implementation (which calls
        # readinto() internally).
        rawio = self.MockRawIOWithoutRead((b"abc", b"d", None, b"efg", None))
        self.assertEqual(rawio.read(2), b"ab")
        self.assertEqual(rawio.read(2), b"c")
        self.assertEqual(rawio.read(2), b"d")
        self.assertEqual(rawio.read(2), None)
        self.assertEqual(rawio.read(2), b"ef")
        self.assertEqual(rawio.read(2), b"g")
        self.assertEqual(rawio.read(2), None)
        self.assertEqual(rawio.read(2), b"")

    def test_fileio_closefd(self):
        # Issue #4841
        with self.open(__file__, 'rb') as f1, \
             self.open(__file__, 'rb') as f2:
            fileio = self.FileIO(f1.fileno(), closefd=False)
            # .__init__() must not close f1
            fileio.__init__(f2.fileno(), closefd=False)
            f1.readline()
            # .close() must not close f2
            fileio.close()
            f2.readline()

    def test_nonbuffered_textio(self):
        with warnings.catch_warnings(record=True) as recorded:
            with self.assertRaises(ValueError):
                self.open(support.TESTFN, 'w', buffering=0)
            support.gc_collect()
        self.assertEqual(recorded, [])

    def test_invalid_newline(self):
        with warnings.catch_warnings(record=True) as recorded:
            with self.assertRaises(ValueError):
                self.open(support.TESTFN, 'w', newline='invalid')
            support.gc_collect()
        self.assertEqual(recorded, [])


class CIOTest(IOTest):

    def test_IOBase_finalize(self):
        # Issue #12149: segmentation fault on _PyIOBase_finalize when both a
        # class which inherits IOBase and an object of this class are caught
        # in a reference cycle and close() is already in the method cache.
        class MyIO(self.IOBase):
            def close(self):
                pass

        # create an instance to populate the method cache
        MyIO()
        obj = MyIO()
        obj.obj = obj
        wr = weakref.ref(obj)
        del MyIO
        del obj
        support.gc_collect()
        self.assertTrue(wr() is None, wr)

class PyIOTest(IOTest):
    test_array_writes = unittest.skip(
        "len(array.array) returns number of elements rather than bytelength"
    )(IOTest.test_array_writes)


class CommonBufferedTests:
    # Tests common to BufferedReader, BufferedWriter and BufferedRandom

    def test_detach(self):
        raw = self.MockRawIO()
        buf = self.tp(raw)
        self.assertIs(buf.detach(), raw)
        self.assertRaises(ValueError, buf.detach)

    def test_fileno(self):
        rawio = self.MockRawIO()
        bufio = self.tp(rawio)

        self.assertEqual(42, bufio.fileno())

    @unittest.skip('test having existential crisis')
    def test_no_fileno(self):
        # XXX will we always have fileno() function? If so, kill
        # this test. Else, write it.
        pass

    def test_invalid_args(self):
        rawio = self.MockRawIO()
        bufio = self.tp(rawio)
        # Invalid whence
        self.assertRaises(ValueError, bufio.seek, 0, -1)
        self.assertRaises(ValueError, bufio.seek, 0, 3)

    def test_override_destructor(self):
        tp = self.tp
        record = []
        class MyBufferedIO(tp):
            def __del__(self):
                record.append(1)
                try:
                    f = super(MyBufferedIO, self).__del__
                except AttributeError:
                    pass
                else:
                    f()
            def close(self):
                record.append(2)
                super(MyBufferedIO, self).close()
            def flush(self):
                record.append(3)
                super(MyBufferedIO, self).flush()
        rawio = self.MockRawIO()
        bufio = MyBufferedIO(rawio)
        writable = bufio.writable()
        del bufio
        support.gc_collect()
        if writable:
            self.assertEqual(record, [1, 2, 3])
        else:
            self.assertEqual(record, [1, 2])

    def test_context_manager(self):
        # Test usability as a context manager
        rawio = self.MockRawIO()
        bufio = self.tp(rawio)
        def _with():
            with bufio:
                pass
        _with()
        # bufio should now be closed, and using it a second time should raise
        # a ValueError.
        self.assertRaises(ValueError, _with)

    def test_error_through_destructor(self):
        # Test that the exception state is not modified by a destructor,
        # even if close() fails.
        rawio = self.CloseFailureIO()
        def f():
            self.tp(rawio).xyzzy
        with support.captured_output("stderr") as s:
            self.assertRaises(AttributeError, f)
        s = s.getvalue().strip()
        if s:
            # The destructor *may* have printed an unraisable error, check it
            self.assertEqual(len(s.splitlines()), 1)
            self.assertTrue(s.startswith("Exception IOError: "), s)
            self.assertTrue(s.endswith(" ignored"), s)

    def test_repr(self):
        raw = self.MockRawIO()
        b = self.tp(raw)
        clsname = "%s.%s" % (self.tp.__module__, self.tp.__name__)
        self.assertEqual(repr(b), "<%s>" % clsname)
        raw.name = "dummy"
        self.assertEqual(repr(b), "<%s name=u'dummy'>" % clsname)
        raw.name = b"dummy"
        self.assertEqual(repr(b), "<%s name='dummy'>" % clsname)

    def test_flush_error_on_close(self):
        raw = self.MockRawIO()
        def bad_flush():
            raise IOError()
        raw.flush = bad_flush
        b = self.tp(raw)
        self.assertRaises(IOError, b.close) # exception not swallowed
        self.assertTrue(b.closed)

    def test_close_error_on_close(self):
        raw = self.MockRawIO()
        def bad_flush():
            raise IOError('flush')
        def bad_close():
            raise IOError('close')
        raw.close = bad_close
        b = self.tp(raw)
        b.flush = bad_flush
        with self.assertRaises(IOError) as err: # exception not swallowed
            b.close()
        self.assertEqual(err.exception.args, ('close',))
        self.assertFalse(b.closed)

    def test_multi_close(self):
        raw = self.MockRawIO()
        b = self.tp(raw)
        b.close()
        b.close()
        b.close()
        self.assertRaises(ValueError, b.flush)

    def test_readonly_attributes(self):
        raw = self.MockRawIO()
        buf = self.tp(raw)
        x = self.MockRawIO()
        with self.assertRaises((AttributeError, TypeError)):
            buf.raw = x


class SizeofTest:

    @support.cpython_only
    def test_sizeof(self):
        bufsize1 = 4096
        bufsize2 = 8192
        rawio = self.MockRawIO()
        bufio = self.tp(rawio, buffer_size=bufsize1)
        size = sys.getsizeof(bufio) - bufsize1
        rawio = self.MockRawIO()
        bufio = self.tp(rawio, buffer_size=bufsize2)
        self.assertEqual(sys.getsizeof(bufio), size + bufsize2)


class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
    read_mode = "rb"

    def test_constructor(self):
        rawio = self.MockRawIO([b"abc"])
        bufio = self.tp(rawio)
        bufio.__init__(rawio)
        bufio.__init__(rawio, buffer_size=1024)
        bufio.__init__(rawio, buffer_size=16)
        self.assertEqual(b"abc", bufio.read())
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
        rawio = self.MockRawIO([b"abc"])
        bufio.__init__(rawio)
        self.assertEqual(b"abc", bufio.read())

    def test_uninitialized(self):
        bufio = self.tp.__new__(self.tp)
        del bufio
        bufio = self.tp.__new__(self.tp)
        self.assertRaisesRegexp((ValueError, AttributeError),
                                'uninitialized|has no attribute',
                                bufio.read, 0)
        bufio.__init__(self.MockRawIO())
        self.assertEqual(bufio.read(0), b'')

    def test_read(self):
        for arg in (None, 7):
            rawio = self.MockRawIO((b"abc", b"d", b"efg"))
            bufio = self.tp(rawio)
            self.assertEqual(b"abcdefg", bufio.read(arg))
        # Invalid args
        self.assertRaises(ValueError, bufio.read, -2)

    def test_read1(self):
        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
        bufio = self.tp(rawio)
        self.assertEqual(b"a", bufio.read(1))
        self.assertEqual(b"b", bufio.read1(1))
        self.assertEqual(rawio._reads, 1)
        self.assertEqual(b"c", bufio.read1(100))
        self.assertEqual(rawio._reads, 1)
        self.assertEqual(b"d", bufio.read1(100))
        self.assertEqual(rawio._reads, 2)
        self.assertEqual(b"efg", bufio.read1(100))
        self.assertEqual(rawio._reads, 3)
        self.assertEqual(b"", bufio.read1(100))
        self.assertEqual(rawio._reads, 4)
        # Invalid args
        self.assertRaises(ValueError, bufio.read1, -1)

    def test_readinto(self):
        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
        bufio = self.tp(rawio)
        b = bytearray(2)
        self.assertEqual(bufio.readinto(b), 2)
        self.assertEqual(b, b"ab")
        self.assertEqual(bufio.readinto(b), 2)
        self.assertEqual(b, b"cd")
        self.assertEqual(bufio.readinto(b), 2)
        self.assertEqual(b, b"ef")
        self.assertEqual(bufio.readinto(b), 1)
        self.assertEqual(b, b"gf")
        self.assertEqual(bufio.readinto(b), 0)
        self.assertEqual(b, b"gf")

    def test_readlines(self):
        def bufio():
            rawio = self.MockRawIO((b"abc\n", b"d\n", b"ef"))
            return self.tp(rawio)
        self.assertEqual(bufio().readlines(), [b"abc\n", b"d\n", b"ef"])
        self.assertEqual(bufio().readlines(5), [b"abc\n", b"d\n"])
        self.assertEqual(bufio().readlines(None), [b"abc\n", b"d\n", b"ef"])

    def test_buffering(self):
        data = b"abcdefghi"
        dlen = len(data)

        tests = [
            [ 100, [ 3, 1, 4, 8 ], [ dlen, 0 ] ],
            [ 100, [ 3, 3, 3],     [ dlen ]    ],
            [   4, [ 1, 2, 4, 2 ], [ 4, 4, 1 ] ],
        ]

        for bufsize, buf_read_sizes, raw_read_sizes in tests:
            rawio = self.MockFileIO(data)
            bufio = self.tp(rawio, buffer_size=bufsize)
            pos = 0
            for nbytes in buf_read_sizes:
                self.assertEqual(bufio.read(nbytes), data[pos:pos+nbytes])
                pos += nbytes
            # this is mildly implementation-dependent
            self.assertEqual(rawio.read_history, raw_read_sizes)

    def test_read_non_blocking(self):
        # Inject some None's in there to simulate EWOULDBLOCK
        rawio = self.MockRawIO((b"abc", b"d", None, b"efg", None, None, None))
        bufio = self.tp(rawio)
        self.assertEqual(b"abcd", bufio.read(6))
        self.assertEqual(b"e", bufio.read(1))
        self.assertEqual(b"fg", bufio.read())
        self.assertEqual(b"", bufio.peek(1))
        self.assertIsNone(bufio.read())
        self.assertEqual(b"", bufio.read())

        rawio = self.MockRawIO((b"a", None, None))
        self.assertEqual(b"a", rawio.readall())
        self.assertIsNone(rawio.readall())

    def test_read_past_eof(self):
        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
        bufio = self.tp(rawio)

        self.assertEqual(b"abcdefg", bufio.read(9000))

    def test_read_all(self):
        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
        bufio = self.tp(rawio)

        self.assertEqual(b"abcdefg", bufio.read())

    @unittest.skipUnless(threading, 'Threading required for this test.')
    @support.requires_resource('cpu')
    def test_threads(self):
        try:
            # Write out many bytes with exactly the same number of 0's,
            # 1's... 255's. This will help us check that concurrent reading
            # doesn't duplicate or forget contents.
            N = 1000
            l = list(range(256)) * N
            random.shuffle(l)
            s = bytes(bytearray(l))
            with self.open(support.TESTFN, "wb") as f:
                f.write(s)
            with self.open(support.TESTFN, self.read_mode, buffering=0) as raw:
                bufio = self.tp(raw, 8)
                errors = []
                results = []
                def f():
                    try:
                        # Intra-buffer read then buffer-flushing read
                        for n in cycle([1, 19]):
                            s = bufio.read(n)
                            if not s:
                                break
                            # list.append() is atomic
                            results.append(s)
                    except Exception as e:
                        errors.append(e)
                        raise
                threads = [threading.Thread(target=f) for x in range(20)]
                for t in threads:
                    t.start()
                time.sleep(0.02) # yield
                for t in threads:
                    t.join()
                self.assertFalse(errors,
                    "the following exceptions were caught: %r" % errors)
                s = b''.join(results)
                for i in range(256):
                    c = bytes(bytearray([i]))
                    self.assertEqual(s.count(c), N)
        finally:
            support.unlink(support.TESTFN)

    def test_misbehaved_io(self):
        rawio = self.MisbehavedRawIO((b"abc", b"d", b"efg"))
        bufio = self.tp(rawio)
        self.assertRaises(IOError, bufio.seek, 0)
        self.assertRaises(IOError, bufio.tell)

    def test_no_extraneous_read(self):
        # Issue #9550; when the raw IO object has satisfied the read request,
        # we should not issue any additional reads, otherwise it may block
        # (e.g. socket).
        bufsize = 16
        for n in (2, bufsize - 1, bufsize, bufsize + 1, bufsize * 2):
            rawio = self.MockRawIO([b"x" * n])
            bufio = self.tp(rawio, bufsize)
            self.assertEqual(bufio.read(n), b"x" * n)
            # Simple case: one raw read is enough to satisfy the request.
            self.assertEqual(rawio._extraneous_reads, 0,
                             "failed for {}: {} != 0".format(n, rawio._extraneous_reads))
            # A more complex case where two raw reads are needed to satisfy
            # the request.
            rawio = self.MockRawIO([b"x" * (n - 1), b"x"])
            bufio = self.tp(rawio, bufsize)
            self.assertEqual(bufio.read(n), b"x" * n)
            self.assertEqual(rawio._extraneous_reads, 0,
                             "failed for {}: {} != 0".format(n, rawio._extraneous_reads))


class CBufferedReaderTest(BufferedReaderTest, SizeofTest):
    tp = io.BufferedReader

    def test_constructor(self):
        BufferedReaderTest.test_constructor(self)
        # The allocation can succeed on 32-bit builds, e.g. with more
        # than 2GB RAM and a 64-bit kernel.
        if sys.maxsize > 0x7FFFFFFF:
            rawio = self.MockRawIO()
            bufio = self.tp(rawio)
            self.assertRaises((OverflowError, MemoryError, ValueError),
                bufio.__init__, rawio, sys.maxsize)

    def test_initialization(self):
        rawio = self.MockRawIO([b"abc"])
        bufio = self.tp(rawio)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
        self.assertRaises(ValueError, bufio.read)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
        self.assertRaises(ValueError, bufio.read)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
        self.assertRaises(ValueError, bufio.read)

    def test_misbehaved_io_read(self):
        rawio = self.MisbehavedRawIO((b"abc", b"d", b"efg"))
        bufio = self.tp(rawio)
        # _pyio.BufferedReader seems to implement reading different, so that
        # checking this is not so easy.
        self.assertRaises(IOError, bufio.read, 10)

    def test_garbage_collection(self):
        # C BufferedReader objects are collected.
        # The Python version has __del__, so it ends into gc.garbage instead
        rawio = self.FileIO(support.TESTFN, "w+b")
        f = self.tp(rawio)
        f.f = f
        wr = weakref.ref(f)
        del f
        support.gc_collect()
        self.assertTrue(wr() is None, wr)

    def test_args_error(self):
        # Issue #17275
        with self.assertRaisesRegexp(TypeError, "BufferedReader"):
            self.tp(io.BytesIO(), 1024, 1024, 1024)


class PyBufferedReaderTest(BufferedReaderTest):
    tp = pyio.BufferedReader


class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
    write_mode = "wb"

    def test_constructor(self):
        rawio = self.MockRawIO()
        bufio = self.tp(rawio)
        bufio.__init__(rawio)
        bufio.__init__(rawio, buffer_size=1024)
        bufio.__init__(rawio, buffer_size=16)
        self.assertEqual(3, bufio.write(b"abc"))
        bufio.flush()
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
        bufio.__init__(rawio)
        self.assertEqual(3, bufio.write(b"ghi"))
        bufio.flush()
        self.assertEqual(b"".join(rawio._write_stack), b"abcghi")

    def test_uninitialized(self):
        bufio = self.tp.__new__(self.tp)
        del bufio
        bufio = self.tp.__new__(self.tp)
        self.assertRaisesRegexp((ValueError, AttributeError),
                                'uninitialized|has no attribute',
                                bufio.write, b'')
        bufio.__init__(self.MockRawIO())
        self.assertEqual(bufio.write(b''), 0)

    def test_detach_flush(self):
        raw = self.MockRawIO()
        buf = self.tp(raw)
        buf.write(b"howdy!")
        self.assertFalse(raw._write_stack)
        buf.detach()
        self.assertEqual(raw._write_stack, [b"howdy!"])

    def test_write(self):
        # Write to the buffered IO but don't overflow the buffer.
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        bufio.write(b"abc")
        self.assertFalse(writer._write_stack)

    def test_write_overflow(self):
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        contents = b"abcdefghijklmnop"
        for n in range(0, len(contents), 3):
            bufio.write(contents[n:n+3])
        flushed = b"".join(writer._write_stack)
        # At least (total - 8) bytes were implicitly flushed, perhaps more
        # depending on the implementation.
        self.assertTrue(flushed.startswith(contents[:-8]), flushed)

    def check_writes(self, intermediate_func):
        # Lots of writes, test the flushed output is as expected.
        contents = bytes(range(256)) * 1000
        n = 0
        writer = self.MockRawIO()
        bufio = self.tp(writer, 13)
        # Generator of write sizes: repeat each N 15 times then proceed to N+1
        def gen_sizes():
            for size in count(1):
                for i in range(15):
                    yield size
        sizes = gen_sizes()
        while n < len(contents):
            size = min(next(sizes), len(contents) - n)
            self.assertEqual(bufio.write(contents[n:n+size]), size)
            intermediate_func(bufio)
            n += size
        bufio.flush()
        self.assertEqual(contents,
            b"".join(writer._write_stack))

    def test_writes(self):
        self.check_writes(lambda bufio: None)

    def test_writes_and_flushes(self):
        self.check_writes(lambda bufio: bufio.flush())

    def test_writes_and_seeks(self):
        def _seekabs(bufio):
            pos = bufio.tell()
            bufio.seek(pos + 1, 0)
            bufio.seek(pos - 1, 0)
            bufio.seek(pos, 0)
        self.check_writes(_seekabs)
        def _seekrel(bufio):
            pos = bufio.seek(0, 1)
            bufio.seek(+1, 1)
            bufio.seek(-1, 1)
            bufio.seek(pos, 0)
        self.check_writes(_seekrel)

    def test_writes_and_truncates(self):
        self.check_writes(lambda bufio: bufio.truncate(bufio.tell()))

    def test_write_non_blocking(self):
        raw = self.MockNonBlockWriterIO()
        bufio = self.tp(raw, 8)

        self.assertEqual(bufio.write(b"abcd"), 4)
        self.assertEqual(bufio.write(b"efghi"), 5)
        # 1 byte will be written, the rest will be buffered
        raw.block_on(b"k")
        self.assertEqual(bufio.write(b"jklmn"), 5)

        # 8 bytes will be written, 8 will be buffered and the rest will be lost
        raw.block_on(b"0")
        try:
            bufio.write(b"opqrwxyz0123456789")
        except self.BlockingIOError as e:
            written = e.characters_written
        else:
            self.fail("BlockingIOError should have been raised")
        self.assertEqual(written, 16)
        self.assertEqual(raw.pop_written(),
            b"abcdefghijklmnopqrwxyz")

        self.assertEqual(bufio.write(b"ABCDEFGHI"), 9)
        s = raw.pop_written()
        # Previously buffered bytes were flushed
        self.assertTrue(s.startswith(b"01234567A"), s)

    def test_write_and_rewind(self):
        raw = io.BytesIO()
        bufio = self.tp(raw, 4)
        self.assertEqual(bufio.write(b"abcdef"), 6)
        self.assertEqual(bufio.tell(), 6)
        bufio.seek(0, 0)
        self.assertEqual(bufio.write(b"XY"), 2)
        bufio.seek(6, 0)
        self.assertEqual(raw.getvalue(), b"XYcdef")
        self.assertEqual(bufio.write(b"123456"), 6)
        bufio.flush()
        self.assertEqual(raw.getvalue(), b"XYcdef123456")

    def test_flush(self):
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        bufio.write(b"abc")
        bufio.flush()
        self.assertEqual(b"abc", writer._write_stack[0])

    def test_writelines(self):
        l = [b'ab', b'cd', b'ef']
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        bufio.writelines(l)
        bufio.flush()
        self.assertEqual(b''.join(writer._write_stack), b'abcdef')

    def test_writelines_userlist(self):
        l = UserList([b'ab', b'cd', b'ef'])
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        bufio.writelines(l)
        bufio.flush()
        self.assertEqual(b''.join(writer._write_stack), b'abcdef')

    def test_writelines_error(self):
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        self.assertRaises(TypeError, bufio.writelines, [1, 2, 3])
        self.assertRaises(TypeError, bufio.writelines, None)

    def test_destructor(self):
        writer = self.MockRawIO()
        bufio = self.tp(writer, 8)
        bufio.write(b"abc")
        del bufio
        support.gc_collect()
        self.assertEqual(b"abc", writer._write_stack[0])

    def test_truncate(self):
        # Truncate implicitly flushes the buffer.
        with self.open(support.TESTFN, self.write_mode, buffering=0) as raw:
            bufio = self.tp(raw, 8)
            bufio.write(b"abcdef")
            self.assertEqual(bufio.truncate(3), 3)
            self.assertEqual(bufio.tell(), 6)
        with self.open(support.TESTFN, "rb", buffering=0) as f:
            self.assertEqual(f.read(), b"abc")

    @unittest.skipUnless(threading, 'Threading required for this test.')
    @support.requires_resource('cpu')
    def test_threads(self):
        try:
            # Write out many bytes from many threads and test they were
            # all flushed.
            N = 1000
            contents = bytes(range(256)) * N
            sizes = cycle([1, 19])
            n = 0
            queue = deque()
            while n < len(contents):
                size = next(sizes)
                queue.append(contents[n:n+size])
                n += size
            del contents
            # We use a real file object because it allows us to
            # exercise situations where the GIL is released before
            # writing the buffer to the raw streams. This is in addition
            # to concurrency issues due to switching threads in the middle
            # of Python code.
            with self.open(support.TESTFN, self.write_mode, buffering=0) as raw:
                bufio = self.tp(raw, 8)
                errors = []
                def f():
                    try:
                        while True:
                            try:
                                s = queue.popleft()
                            except IndexError:
                                return
                            bufio.write(s)
                    except Exception as e:
                        errors.append(e)
                        raise
                threads = [threading.Thread(target=f) for x in range(20)]
                for t in threads:
                    t.start()
                time.sleep(0.02) # yield
                for t in threads:
                    t.join()
                self.assertFalse(errors,
                    "the following exceptions were caught: %r" % errors)
                bufio.close()
            with self.open(support.TESTFN, "rb") as f:
                s = f.read()
            for i in range(256):
                self.assertEqual(s.count(bytes([i])), N)
        finally:
            support.unlink(support.TESTFN)

    def test_misbehaved_io(self):
        rawio = self.MisbehavedRawIO()
        bufio = self.tp(rawio, 5)
        self.assertRaises(IOError, bufio.seek, 0)
        self.assertRaises(IOError, bufio.tell)
        self.assertRaises(IOError, bufio.write, b"abcdef")

    def test_max_buffer_size_deprecation(self):
        with support.check_warnings(("max_buffer_size is deprecated",
                                     DeprecationWarning)):
            self.tp(self.MockRawIO(), 8, 12)

    def test_write_error_on_close(self):
        raw = self.MockRawIO()
        def bad_write(b):
            raise IOError()
        raw.write = bad_write
        b = self.tp(raw)
        b.write(b'spam')
        self.assertRaises(IOError, b.close) # exception not swallowed
        self.assertTrue(b.closed)


class CBufferedWriterTest(BufferedWriterTest, SizeofTest):
    tp = io.BufferedWriter

    def test_constructor(self):
        BufferedWriterTest.test_constructor(self)
        # The allocation can succeed on 32-bit builds, e.g. with more
        # than 2GB RAM and a 64-bit kernel.
        if sys.maxsize > 0x7FFFFFFF:
            rawio = self.MockRawIO()
            bufio = self.tp(rawio)
            self.assertRaises((OverflowError, MemoryError, ValueError),
                bufio.__init__, rawio, sys.maxsize)

    def test_initialization(self):
        rawio = self.MockRawIO()
        bufio = self.tp(rawio)
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
        self.assertRaises(ValueError, bufio.write, b"def")
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
        self.assertRaises(ValueError, bufio.write, b"def")
        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
        self.assertRaises(ValueError, bufio.write, b"def")

    def test_garbage_collection(self):
        # C BufferedWriter objects are collected, and collecting them flushes
        # all data to disk.
        # The Python version has __del__, so it ends into gc.garbage instead
        rawio = self.FileIO(support.TESTFN, "w+b")
        f = self.tp(rawio)
        f.write(b"123xxx")
        f.x = f
        wr = weakref.ref(f)
        del f
        support.gc_collect()
        self.assertTrue(wr() is None, wr)
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.read(), b"123xxx")

    def test_args_error(self):
        # Issue #17275
        with self.assertRaisesRegexp(TypeError, "BufferedWriter"):
            self.tp(io.BytesIO(), 1024, 1024, 1024)


class PyBufferedWriterTest(BufferedWriterTest):
    tp = pyio.BufferedWriter

class BufferedRWPairTest(unittest.TestCase):

    def test_constructor(self):
        pair = self.tp(self.MockRawIO(), self.MockRawIO())
        self.assertFalse(pair.closed)

    def test_uninitialized(self):
        pair = self.tp.__new__(self.tp)
        del pair
        pair = self.tp.__new__(self.tp)
        self.assertRaisesRegexp((ValueError, AttributeError),
                                'uninitialized|has no attribute',
                                pair.read, 0)
        self.assertRaisesRegexp((ValueError, AttributeError),
                                'uninitialized|has no attribute',
                                pair.write, b'')
        pair.__init__(self.MockRawIO(), self.MockRawIO())
        self.assertEqual(pair.read(0), b'')
        self.assertEqual(pair.write(b''), 0)

    def test_detach(self):
        pair = self.tp(self.MockRawIO(), self.MockRawIO())
        self.assertRaises(self.UnsupportedOperation, pair.detach)

    def test_constructor_max_buffer_size_deprecation(self):
        with support.check_warnings(("max_buffer_size is deprecated",
                                     DeprecationWarning)):
            self.tp(self.MockRawIO(), self.MockRawIO(), 8, 12)

    def test_constructor_with_not_readable(self):
        class NotReadable(MockRawIO):
            def readable(self):
                return False

        self.assertRaises(IOError, self.tp, NotReadable(), self.MockRawIO())

    def test_constructor_with_not_writeable(self):
        class NotWriteable(MockRawIO):
            def writable(self):
                return False

        self.assertRaises(IOError, self.tp, self.MockRawIO(), NotWriteable())

    def test_read(self):
        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())

        self.assertEqual(pair.read(3), b"abc")
        self.assertEqual(pair.read(1), b"d")
        self.assertEqual(pair.read(), b"ef")
        pair = self.tp(self.BytesIO(b"abc"), self.MockRawIO())
        self.assertEqual(pair.read(None), b"abc")

    def test_readlines(self):
        pair = lambda: self.tp(self.BytesIO(b"abc\ndef\nh"), self.MockRawIO())
        self.assertEqual(pair().readlines(), [b"abc\n", b"def\n", b"h"])
        self.assertEqual(pair().readlines(), [b"abc\n", b"def\n", b"h"])
        self.assertEqual(pair().readlines(5), [b"abc\n", b"def\n"])

    def test_read1(self):
        # .read1() is delegated to the underlying reader object, so this test
        # can be shallow.
        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())

        self.assertEqual(pair.read1(3), b"abc")

    def test_readinto(self):
        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())

        data = bytearray(5)
        self.assertEqual(pair.readinto(data), 5)
        self.assertEqual(data, b"abcde")

    def test_write(self):
        w = self.MockRawIO()
        pair = self.tp(self.MockRawIO(), w)

        pair.write(b"abc")
        pair.flush()
        pair.write(b"def")
        pair.flush()
        self.assertEqual(w._write_stack, [b"abc", b"def"])

    def test_peek(self):
        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())

        self.assertTrue(pair.peek(3).startswith(b"abc"))
        self.assertEqual(pair.read(3), b"abc")

    def test_readable(self):
        pair = self.tp(self.MockRawIO(), self.MockRawIO())
        self.assertTrue(pair.readable())

    def test_writeable(self):
        pair = self.tp(self.MockRawIO(), self.MockRawIO())
        self.assertTrue(pair.writable())

    def test_seekable(self):
        # BufferedRWPairs are never seekable, even if their readers and writers
        # are.
        pair = self.tp(self.MockRawIO(), self.MockRawIO())
        self.assertFalse(pair.seekable())

    # .flush() is delegated to the underlying writer object and has been
    # tested in the test_write method.

    def test_close_and_closed(self):
        pair = self.tp(self.MockRawIO(), self.MockRawIO())
        self.assertFalse(pair.closed)
        pair.close()
        self.assertTrue(pair.closed)

    def test_isatty(self):
        class SelectableIsAtty(MockRawIO):
            def __init__(self, isatty):
                MockRawIO.__init__(self)
                self._isatty = isatty

            def isatty(self):
                return self._isatty

        pair = self.tp(SelectableIsAtty(False), SelectableIsAtty(False))
        self.assertFalse(pair.isatty())

        pair = self.tp(SelectableIsAtty(True), SelectableIsAtty(False))
        self.assertTrue(pair.isatty())

        pair = self.tp(SelectableIsAtty(False), SelectableIsAtty(True))
        self.assertTrue(pair.isatty())

        pair = self.tp(SelectableIsAtty(True), SelectableIsAtty(True))
        self.assertTrue(pair.isatty())

class CBufferedRWPairTest(BufferedRWPairTest):
    tp = io.BufferedRWPair

class PyBufferedRWPairTest(BufferedRWPairTest):
    tp = pyio.BufferedRWPair


class BufferedRandomTest(BufferedReaderTest, BufferedWriterTest):
    read_mode = "rb+"
    write_mode = "wb+"

    def test_constructor(self):
        BufferedReaderTest.test_constructor(self)
        BufferedWriterTest.test_constructor(self)

    def test_uninitialized(self):
        BufferedReaderTest.test_uninitialized(self)
        BufferedWriterTest.test_uninitialized(self)

    def test_read_and_write(self):
        raw = self.MockRawIO((b"asdf", b"ghjk"))
        rw = self.tp(raw, 8)

        self.assertEqual(b"as", rw.read(2))
        rw.write(b"ddd")
        rw.write(b"eee")
        self.assertFalse(raw._write_stack) # Buffer writes
        self.assertEqual(b"ghjk", rw.read())
        self.assertEqual(b"dddeee", raw._write_stack[0])

    def test_seek_and_tell(self):
        raw = self.BytesIO(b"asdfghjkl")
        rw = self.tp(raw)

        self.assertEqual(b"as", rw.read(2))
        self.assertEqual(2, rw.tell())
        rw.seek(0, 0)
        self.assertEqual(b"asdf", rw.read(4))

        rw.write(b"123f")
        rw.seek(0, 0)
        self.assertEqual(b"asdf123fl", rw.read())
        self.assertEqual(9, rw.tell())
        rw.seek(-4, 2)
        self.assertEqual(5, rw.tell())
        rw.seek(2, 1)
        self.assertEqual(7, rw.tell())
        self.assertEqual(b"fl", rw.read(11))
        rw.flush()
        self.assertEqual(b"asdf123fl", raw.getvalue())

        self.assertRaises(TypeError, rw.seek, 0.0)

    def check_flush_and_read(self, read_func):
        raw = self.BytesIO(b"abcdefghi")
        bufio = self.tp(raw)

        self.assertEqual(b"ab", read_func(bufio, 2))
        bufio.write(b"12")
        self.assertEqual(b"ef", read_func(bufio, 2))
        self.assertEqual(6, bufio.tell())
        bufio.flush()
        self.assertEqual(6, bufio.tell())
        self.assertEqual(b"ghi", read_func(bufio))
        raw.seek(0, 0)
        raw.write(b"XYZ")
        # flush() resets the read buffer
        bufio.flush()
        bufio.seek(0, 0)
        self.assertEqual(b"XYZ", read_func(bufio, 3))

    def test_flush_and_read(self):
        self.check_flush_and_read(lambda bufio, *args: bufio.read(*args))

    def test_flush_and_readinto(self):
        def _readinto(bufio, n=-1):
            b = bytearray(n if n >= 0 else 9999)
            n = bufio.readinto(b)
            return bytes(b[:n])
        self.check_flush_and_read(_readinto)

    def test_flush_and_peek(self):
        def _peek(bufio, n=-1):
            # This relies on the fact that the buffer can contain the whole
            # raw stream, otherwise peek() can return less.
            b = bufio.peek(n)
            if n != -1:
                b = b[:n]
            bufio.seek(len(b), 1)
            return b
        self.check_flush_and_read(_peek)

    def test_flush_and_write(self):
        raw = self.BytesIO(b"abcdefghi")
        bufio = self.tp(raw)

        bufio.write(b"123")
        bufio.flush()
        bufio.write(b"45")
        bufio.flush()
        bufio.seek(0, 0)
        self.assertEqual(b"12345fghi", raw.getvalue())
        self.assertEqual(b"12345fghi", bufio.read())

    def test_threads(self):
        BufferedReaderTest.test_threads(self)
        BufferedWriterTest.test_threads(self)

    def test_writes_and_peek(self):
        def _peek(bufio):
            bufio.peek(1)
        self.check_writes(_peek)
        def _peek(bufio):
            pos = bufio.tell()
            bufio.seek(-1, 1)
            bufio.peek(1)
            bufio.seek(pos, 0)
        self.check_writes(_peek)

    def test_writes_and_reads(self):
        def _read(bufio):
            bufio.seek(-1, 1)
            bufio.read(1)
        self.check_writes(_read)

    def test_writes_and_read1s(self):
        def _read1(bufio):
            bufio.seek(-1, 1)
            bufio.read1(1)
        self.check_writes(_read1)

    def test_writes_and_readintos(self):
        def _read(bufio):
            bufio.seek(-1, 1)
            bufio.readinto(bytearray(1))
        self.check_writes(_read)

    def test_write_after_readahead(self):
        # Issue #6629: writing after the buffer was filled by readahead should
        # first rewind the raw stream.
        for overwrite_size in [1, 5]:
            raw = self.BytesIO(b"A" * 10)
            bufio = self.tp(raw, 4)
            # Trigger readahead
            self.assertEqual(bufio.read(1), b"A")
            self.assertEqual(bufio.tell(), 1)
            # Overwriting should rewind the raw stream if it needs so
            bufio.write(b"B" * overwrite_size)
            self.assertEqual(bufio.tell(), overwrite_size + 1)
            # If the write size was smaller than the buffer size, flush() and
            # check that rewind happens.
            bufio.flush()
            self.assertEqual(bufio.tell(), overwrite_size + 1)
            s = raw.getvalue()
            self.assertEqual(s,
                b"A" + b"B" * overwrite_size + b"A" * (9 - overwrite_size))

    def test_write_rewind_write(self):
        # Various combinations of reading / writing / seeking backwards / writing again
        def mutate(bufio, pos1, pos2):
            assert pos2 >= pos1
            # Fill the buffer
            bufio.seek(pos1)
            bufio.read(pos2 - pos1)
            bufio.write(b'\x02')
            # This writes earlier than the previous write, but still inside
            # the buffer.
            bufio.seek(pos1)
            bufio.write(b'\x01')

        b = b"\x80\x81\x82\x83\x84"
        for i in range(0, len(b)):
            for j in range(i, len(b)):
                raw = self.BytesIO(b)
                bufio = self.tp(raw, 100)
                mutate(bufio, i, j)
                bufio.flush()
                expected = bytearray(b)
                expected[j] = 2
                expected[i] = 1
                self.assertEqual(raw.getvalue(), expected,
                                 "failed result for i=%d, j=%d" % (i, j))

    def test_truncate_after_read_or_write(self):
        raw = self.BytesIO(b"A" * 10)
        bufio = self.tp(raw, 100)
        self.assertEqual(bufio.read(2), b"AA") # the read buffer gets filled
        self.assertEqual(bufio.truncate(), 2)
        self.assertEqual(bufio.write(b"BB"), 2) # the write buffer increases
        self.assertEqual(bufio.truncate(), 4)

    def test_misbehaved_io(self):
        BufferedReaderTest.test_misbehaved_io(self)
        BufferedWriterTest.test_misbehaved_io(self)

    def test_interleaved_read_write(self):
        # Test for issue #12213
        with self.BytesIO(b'abcdefgh') as raw:
            with self.tp(raw, 100) as f:
                f.write(b"1")
                self.assertEqual(f.read(1), b'b')
                f.write(b'2')
                self.assertEqual(f.read1(1), b'd')
                f.write(b'3')
                buf = bytearray(1)
                f.readinto(buf)
                self.assertEqual(buf, b'f')
                f.write(b'4')
                self.assertEqual(f.peek(1), b'h')
                f.flush()
                self.assertEqual(raw.getvalue(), b'1b2d3f4h')

        with self.BytesIO(b'abc') as raw:
            with self.tp(raw, 100) as f:
                self.assertEqual(f.read(1), b'a')
                f.write(b"2")
                self.assertEqual(f.read(1), b'c')
                f.flush()
                self.assertEqual(raw.getvalue(), b'a2c')

    def test_interleaved_readline_write(self):
        with self.BytesIO(b'ab\ncdef\ng\n') as raw:
            with self.tp(raw) as f:
                f.write(b'1')
                self.assertEqual(f.readline(), b'b\n')
                f.write(b'2')
                self.assertEqual(f.readline(), b'def\n')
                f.write(b'3')
                self.assertEqual(f.readline(), b'\n')
                f.flush()
                self.assertEqual(raw.getvalue(), b'1b\n2def\n3\n')


class CBufferedRandomTest(CBufferedReaderTest, CBufferedWriterTest,
                          BufferedRandomTest, SizeofTest):
    tp = io.BufferedRandom

    def test_constructor(self):
        BufferedRandomTest.test_constructor(self)
        # The allocation can succeed on 32-bit builds, e.g. with more
        # than 2GB RAM and a 64-bit kernel.
        if sys.maxsize > 0x7FFFFFFF:
            rawio = self.MockRawIO()
            bufio = self.tp(rawio)
            self.assertRaises((OverflowError, MemoryError, ValueError),
                bufio.__init__, rawio, sys.maxsize)

    def test_garbage_collection(self):
        CBufferedReaderTest.test_garbage_collection(self)
        CBufferedWriterTest.test_garbage_collection(self)

    def test_args_error(self):
        # Issue #17275
        with self.assertRaisesRegexp(TypeError, "BufferedRandom"):
            self.tp(io.BytesIO(), 1024, 1024, 1024)


class PyBufferedRandomTest(BufferedRandomTest):
    tp = pyio.BufferedRandom


# To fully exercise seek/tell, the StatefulIncrementalDecoder has these
# properties:
#   - A single output character can correspond to many bytes of input.
#   - The number of input bytes to complete the character can be
#     undetermined until the last input byte is received.
#   - The number of input bytes can vary depending on previous input.
#   - A single input byte can correspond to many characters of output.
#   - The number of output characters can be undetermined until the
#     last input byte is received.
#   - The number of output characters can vary depending on previous input.

class StatefulIncrementalDecoder(codecs.IncrementalDecoder):
    """
    For testing seek/tell behavior with a stateful, buffering decoder.

    Input is a sequence of words.  Words may be fixed-length (length set
    by input) or variable-length (period-terminated).  In variable-length
    mode, extra periods are ignored.  Possible words are:
      - 'i' followed by a number sets the input length, I (maximum 99).
        When I is set to 0, words are space-terminated.
      - 'o' followed by a number sets the output length, O (maximum 99).
      - Any other word is converted into a word followed by a period on
        the output.  The output word consists of the input word truncated
        or padded out with hyphens to make its length equal to O.  If O
        is 0, the word is output verbatim without truncating or padding.
    I and O are initially set to 1.  When I changes, any buffered input is
    re-scanned according to the new I.  EOF also terminates the last word.
    """

    def __init__(self, errors='strict'):
        codecs.IncrementalDecoder.__init__(self, errors)
        self.reset()

    def __repr__(self):
        return '<SID %x>' % id(self)

    def reset(self):
        self.i = 1
        self.o = 1
        self.buffer = bytearray()

    def getstate(self):
        i, o = self.i ^ 1, self.o ^ 1 # so that flags = 0 after reset()
        return bytes(self.buffer), i*100 + o

    def setstate(self, state):
        buffer, io = state
        self.buffer = bytearray(buffer)
        i, o = divmod(io, 100)
        self.i, self.o = i ^ 1, o ^ 1

    def decode(self, input, final=False):
        output = ''
        for b in input:
            if self.i == 0: # variable-length, terminated with period
                if b == '.':
                    if self.buffer:
                        output += self.process_word()
                else:
                    self.buffer.append(b)
            else: # fixed-length, terminate after self.i bytes
                self.buffer.append(b)
                if len(self.buffer) == self.i:
                    output += self.process_word()
        if final and self.buffer: # EOF terminates the last word
            output += self.process_word()
        return output

    def process_word(self):
        output = ''
        if self.buffer[0] == ord('i'):
            self.i = min(99, int(self.buffer[1:] or 0)) # set input length
        elif self.buffer[0] == ord('o'):
            self.o = min(99, int(self.buffer[1:] or 0)) # set output length
        else:
            output = self.buffer.decode('ascii')
            if len(output) < self.o:
                output += '-'*self.o # pad out with hyphens
            if self.o:
                output = output[:self.o] # truncate to output length
            output += '.'
        self.buffer = bytearray()
        return output

    codecEnabled = False

    @classmethod
    def lookupTestDecoder(cls, name):
        if cls.codecEnabled and name == 'test_decoder':
            latin1 = codecs.lookup('latin-1')
            return codecs.CodecInfo(
                name='test_decoder', encode=latin1.encode, decode=None,
                incrementalencoder=None,
                streamreader=None, streamwriter=None,
                incrementaldecoder=cls)

# Register the previous decoder for testing.
# Disabled by default, tests will enable it.
codecs.register(StatefulIncrementalDecoder.lookupTestDecoder)


class StatefulIncrementalDecoderTest(unittest.TestCase):
    """
    Make sure the StatefulIncrementalDecoder actually works.
    """

    test_cases = [
        # I=1, O=1 (fixed-length input == fixed-length output)
        (b'abcd', False, 'a.b.c.d.'),
        # I=0, O=0 (variable-length input, variable-length output)
        (b'oiabcd', True, 'abcd.'),
        # I=0, O=0 (should ignore extra periods)
        (b'oi...abcd...', True, 'abcd.'),
        # I=0, O=6 (variable-length input, fixed-length output)
        (b'i.o6.x.xyz.toolongtofit.', False, 'x-----.xyz---.toolon.'),
        # I=2, O=6 (fixed-length input < fixed-length output)
        (b'i.i2.o6xyz', True, 'xy----.z-----.'),
        # I=6, O=3 (fixed-length input > fixed-length output)
        (b'i.o3.i6.abcdefghijklmnop', True, 'abc.ghi.mno.'),
        # I=0, then 3; O=29, then 15 (with longer output)
        (b'i.o29.a.b.cde.o15.abcdefghijabcdefghij.i3.a.b.c.d.ei00k.l.m', True,
         'a----------------------------.' +
         'b----------------------------.' +
         'cde--------------------------.' +
         'abcdefghijabcde.' +
         'a.b------------.' +
         '.c.------------.' +
         'd.e------------.' +
         'k--------------.' +
         'l--------------.' +
         'm--------------.')
    ]

    def test_decoder(self):
        # Try a few one-shot test cases.
        for input, eof, output in self.test_cases:
            d = StatefulIncrementalDecoder()
            self.assertEqual(d.decode(input, eof), output)

        # Also test an unfinished decode, followed by forcing EOF.
        d = StatefulIncrementalDecoder()
        self.assertEqual(d.decode(b'oiabcd'), '')
        self.assertEqual(d.decode(b'', 1), 'abcd.')

class TextIOWrapperTest(unittest.TestCase):

    def setUp(self):
        self.testdata = b"AAA\r\nBBB\rCCC\r\nDDD\nEEE\r\n"
        self.normalized = b"AAA\nBBB\nCCC\nDDD\nEEE\n".decode("ascii")
        support.unlink(support.TESTFN)

    def tearDown(self):
        support.unlink(support.TESTFN)

    def test_constructor(self):
        r = self.BytesIO(b"\xc3\xa9\n\n")
        b = self.BufferedReader(r, 1000)
        t = self.TextIOWrapper(b)
        t.__init__(b, encoding="latin1", newline="\r\n")
        self.assertEqual(t.encoding, "latin1")
        self.assertEqual(t.line_buffering, False)
        t.__init__(b, encoding="utf8", line_buffering=True)
        self.assertEqual(t.encoding, "utf8")
        self.assertEqual(t.line_buffering, True)
        self.assertEqual("\xe9\n", t.readline())
        self.assertRaises(TypeError, t.__init__, b, newline=42)
        self.assertRaises(ValueError, t.__init__, b, newline='xyzzy')

    def test_detach(self):
        r = self.BytesIO()
        b = self.BufferedWriter(r)
        t = self.TextIOWrapper(b)
        self.assertIs(t.detach(), b)

        t = self.TextIOWrapper(b, encoding="ascii")
        t.write("howdy")
        self.assertFalse(r.getvalue())
        t.detach()
        self.assertEqual(r.getvalue(), b"howdy")
        self.assertRaises(ValueError, t.detach)

    def test_repr(self):
        raw = self.BytesIO("hello".encode("utf-8"))
        b = self.BufferedReader(raw)
        t = self.TextIOWrapper(b, encoding="utf-8")
        modname = self.TextIOWrapper.__module__
        self.assertEqual(repr(t),
                         "<%s.TextIOWrapper encoding='utf-8'>" % modname)
        raw.name = "dummy"
        self.assertEqual(repr(t),
                         "<%s.TextIOWrapper name=u'dummy' encoding='utf-8'>" % modname)
        raw.name = b"dummy"
        self.assertEqual(repr(t),
                         "<%s.TextIOWrapper name='dummy' encoding='utf-8'>" % modname)

    def test_line_buffering(self):
        r = self.BytesIO()
        b = self.BufferedWriter(r, 1000)
        t = self.TextIOWrapper(b, newline="\n", line_buffering=True)
        t.write("X")
        self.assertEqual(r.getvalue(), b"")  # No flush happened
        t.write("Y\nZ")
        self.assertEqual(r.getvalue(), b"XY\nZ")  # All got flushed
        t.write("A\rB")
        self.assertEqual(r.getvalue(), b"XY\nZA\rB")

    def test_encoding(self):
        # Check the encoding attribute is always set, and valid
        b = self.BytesIO()
        t = self.TextIOWrapper(b, encoding="utf8")
        self.assertEqual(t.encoding, "utf8")
        t = self.TextIOWrapper(b)
        self.assertTrue(t.encoding is not None)
        codecs.lookup(t.encoding)

    def test_encoding_errors_reading(self):
        # (1) default
        b = self.BytesIO(b"abc\n\xff\n")
        t = self.TextIOWrapper(b, encoding="ascii")
        self.assertRaises(UnicodeError, t.read)
        # (2) explicit strict
        b = self.BytesIO(b"abc\n\xff\n")
        t = self.TextIOWrapper(b, encoding="ascii", errors="strict")
        self.assertRaises(UnicodeError, t.read)
        # (3) ignore
        b = self.BytesIO(b"abc\n\xff\n")
        t = self.TextIOWrapper(b, encoding="ascii", errors="ignore")
        self.assertEqual(t.read(), "abc\n\n")
        # (4) replace
        b = self.BytesIO(b"abc\n\xff\n")
        t = self.TextIOWrapper(b, encoding="ascii", errors="replace")
        self.assertEqual(t.read(), "abc\n\ufffd\n")

    def test_encoding_errors_writing(self):
        # (1) default
        b = self.BytesIO()
        t = self.TextIOWrapper(b, encoding="ascii")
        self.assertRaises(UnicodeError, t.write, "\xff")
        # (2) explicit strict
        b = self.BytesIO()
        t = self.TextIOWrapper(b, encoding="ascii", errors="strict")
        self.assertRaises(UnicodeError, t.write, "\xff")
        # (3) ignore
        b = self.BytesIO()
        t = self.TextIOWrapper(b, encoding="ascii", errors="ignore",
                             newline="\n")
        t.write("abc\xffdef\n")
        t.flush()
        self.assertEqual(b.getvalue(), b"abcdef\n")
        # (4) replace
        b = self.BytesIO()
        t = self.TextIOWrapper(b, encoding="ascii", errors="replace",
                             newline="\n")
        t.write("abc\xffdef\n")
        t.flush()
        self.assertEqual(b.getvalue(), b"abc?def\n")

    def test_newlines(self):
        input_lines = [ "unix\n", "windows\r\n", "os9\r", "last\n", "nonl" ]

        tests = [
            [ None, [ 'unix\n', 'windows\n', 'os9\n', 'last\n', 'nonl' ] ],
            [ '', input_lines ],
            [ '\n', [ "unix\n", "windows\r\n", "os9\rlast\n", "nonl" ] ],
            [ '\r\n', [ "unix\nwindows\r\n", "os9\rlast\nnonl" ] ],
            [ '\r', [ "unix\nwindows\r", "\nos9\r", "last\nnonl" ] ],
        ]
        encodings = (
            'utf-8', 'latin-1',
            'utf-16', 'utf-16-le', 'utf-16-be',
            'utf-32', 'utf-32-le', 'utf-32-be',
        )

        # Try a range of buffer sizes to test the case where \r is the last
        # character in TextIOWrapper._pending_line.
        for encoding in encodings:
            # XXX: str.encode() should return bytes
            data = bytes(''.join(input_lines).encode(encoding))
            for do_reads in (False, True):
                for bufsize in range(1, 10):
                    for newline, exp_lines in tests:
                        bufio = self.BufferedReader(self.BytesIO(data), bufsize)
                        textio = self.TextIOWrapper(bufio, newline=newline,
                                                  encoding=encoding)
                        if do_reads:
                            got_lines = []
                            while True:
                                c2 = textio.read(2)
                                if c2 == '':
                                    break
                                self.assertEqual(len(c2), 2)
                                got_lines.append(c2 + textio.readline())
                        else:
                            got_lines = list(textio)

                        for got_line, exp_line in zip(got_lines, exp_lines):
                            self.assertEqual(got_line, exp_line)
                        self.assertEqual(len(got_lines), len(exp_lines))

    def test_newlines_input(self):
        testdata = b"AAA\nBB\x00B\nCCC\rDDD\rEEE\r\nFFF\r\nGGG"
        normalized = testdata.replace(b"\r\n", b"\n").replace(b"\r", b"\n")
        for newline, expected in [
            (None, normalized.decode("ascii").splitlines(True)),
            ("", testdata.decode("ascii").splitlines(True)),
            ("\n", ["AAA\n", "BB\x00B\n", "CCC\rDDD\rEEE\r\n", "FFF\r\n", "GGG"]),
            ("\r\n", ["AAA\nBB\x00B\nCCC\rDDD\rEEE\r\n", "FFF\r\n", "GGG"]),
            ("\r",  ["AAA\nBB\x00B\nCCC\r", "DDD\r", "EEE\r", "\nFFF\r", "\nGGG"]),
            ]:
            buf = self.BytesIO(testdata)
            txt = self.TextIOWrapper(buf, encoding="ascii", newline=newline)
            self.assertEqual(txt.readlines(), expected)
            txt.seek(0)
            self.assertEqual(txt.read(), "".join(expected))

    def test_newlines_output(self):
        testdict = {
            "": b"AAA\nBBB\nCCC\nX\rY\r\nZ",
            "\n": b"AAA\nBBB\nCCC\nX\rY\r\nZ",
            "\r": b"AAA\rBBB\rCCC\rX\rY\r\rZ",
            "\r\n": b"AAA\r\nBBB\r\nCCC\r\nX\rY\r\r\nZ",
            }
        tests = [(None, testdict[os.linesep])] + sorted(testdict.items())
        for newline, expected in tests:
            buf = self.BytesIO()
            txt = self.TextIOWrapper(buf, encoding="ascii", newline=newline)
            txt.write("AAA\nB")
            txt.write("BB\nCCC\n")
            txt.write("X\rY\r\nZ")
            txt.flush()
            self.assertEqual(buf.closed, False)
            self.assertEqual(buf.getvalue(), expected)

    def test_destructor(self):
        l = []
        base = self.BytesIO
        class MyBytesIO(base):
            def close(self):
                l.append(self.getvalue())
                base.close(self)
        b = MyBytesIO()
        t = self.TextIOWrapper(b, encoding="ascii")
        t.write("abc")
        del t
        support.gc_collect()
        self.assertEqual([b"abc"], l)

    def test_override_destructor(self):
        record = []
        class MyTextIO(self.TextIOWrapper):
            def __del__(self):
                record.append(1)
                try:
                    f = super(MyTextIO, self).__del__
                except AttributeError:
                    pass
                else:
                    f()
            def close(self):
                record.append(2)
                super(MyTextIO, self).close()
            def flush(self):
                record.append(3)
                super(MyTextIO, self).flush()
        b = self.BytesIO()
        t = MyTextIO(b, encoding="ascii")
        del t
        support.gc_collect()
        self.assertEqual(record, [1, 2, 3])

    def test_error_through_destructor(self):
        # Test that the exception state is not modified by a destructor,
        # even if close() fails.
        rawio = self.CloseFailureIO()
        def f():
            self.TextIOWrapper(rawio).xyzzy
        with support.captured_output("stderr") as s:
            self.assertRaises(AttributeError, f)
        s = s.getvalue().strip()
        if s:
            # The destructor *may* have printed an unraisable error, check it
            self.assertEqual(len(s.splitlines()), 1)
            self.assertTrue(s.startswith("Exception IOError: "), s)
            self.assertTrue(s.endswith(" ignored"), s)

    # Systematic tests of the text I/O API

    def test_basic_io(self):
        for chunksize in (1, 2, 3, 4, 5, 15, 16, 17, 31, 32, 33, 63, 64, 65):
            for enc in "ascii", "latin1", "utf8" :# , "utf-16-be", "utf-16-le":
                f = self.open(support.TESTFN, "w+", encoding=enc)
                f._CHUNK_SIZE = chunksize
                self.assertEqual(f.write("abc"), 3)
                f.close()
                f = self.open(support.TESTFN, "r+", encoding=enc)
                f._CHUNK_SIZE = chunksize
                self.assertEqual(f.tell(), 0)
                self.assertEqual(f.read(), "abc")
                cookie = f.tell()
                self.assertEqual(f.seek(0), 0)
                self.assertEqual(f.read(None), "abc")
                f.seek(0)
                self.assertEqual(f.read(2), "ab")
                self.assertEqual(f.read(1), "c")
                self.assertEqual(f.read(1), "")
                self.assertEqual(f.read(), "")
                self.assertEqual(f.tell(), cookie)
                self.assertEqual(f.seek(0), 0)
                self.assertEqual(f.seek(0, 2), cookie)
                self.assertEqual(f.write("def"), 3)
                self.assertEqual(f.seek(cookie), cookie)
                self.assertEqual(f.read(), "def")
                if enc.startswith("utf"):
                    self.multi_line_test(f, enc)
                f.close()

    def multi_line_test(self, f, enc):
        f.seek(0)
        f.truncate()
        sample = "s\xff\u0fff\uffff"
        wlines = []
        for size in (0, 1, 2, 3, 4, 5, 30, 31, 32, 33, 62, 63, 64, 65, 1000):
            chars = []
            for i in range(size):
                chars.append(sample[i % len(sample)])
            line = "".join(chars) + "\n"
            wlines.append((f.tell(), line))
            f.write(line)
        f.seek(0)
        rlines = []
        while True:
            pos = f.tell()
            line = f.readline()
            if not line:
                break
            rlines.append((pos, line))
        self.assertEqual(rlines, wlines)

    def test_telling(self):
        f = self.open(support.TESTFN, "w+", encoding="utf8")
        p0 = f.tell()
        f.write("\xff\n")
        p1 = f.tell()
        f.write("\xff\n")
        p2 = f.tell()
        f.seek(0)
        self.assertEqual(f.tell(), p0)
        self.assertEqual(f.readline(), "\xff\n")
        self.assertEqual(f.tell(), p1)
        self.assertEqual(f.readline(), "\xff\n")
        self.assertEqual(f.tell(), p2)
        f.seek(0)
        for line in f:
            self.assertEqual(line, "\xff\n")
            self.assertRaises(IOError, f.tell)
        self.assertEqual(f.tell(), p2)
        f.close()

    def test_seeking(self):
        chunk_size = _default_chunk_size()
        prefix_size = chunk_size - 2
        u_prefix = "a" * prefix_size
        prefix = bytes(u_prefix.encode("utf-8"))
        self.assertEqual(len(u_prefix), len(prefix))
        u_suffix = "\u8888\n"
        suffix = bytes(u_suffix.encode("utf-8"))
        line = prefix + suffix
        f = self.open(support.TESTFN, "wb")
        f.write(line*2)
        f.close()
        f = self.open(support.TESTFN, "r", encoding="utf-8")
        s = f.read(prefix_size)
        self.assertEqual(s, prefix.decode("ascii"))
        self.assertEqual(f.tell(), prefix_size)
        self.assertEqual(f.readline(), u_suffix)

    def test_seeking_too(self):
        # Regression test for a specific bug
        data = b'\xe0\xbf\xbf\n'
        f = self.open(support.TESTFN, "wb")
        f.write(data)
        f.close()
        f = self.open(support.TESTFN, "r", encoding="utf-8")
        f._CHUNK_SIZE  # Just test that it exists
        f._CHUNK_SIZE = 2
        f.readline()
        f.tell()

    def test_seek_and_tell(self):
        #Test seek/tell using the StatefulIncrementalDecoder.
        # Make test faster by doing smaller seeks
        CHUNK_SIZE = 128

        def test_seek_and_tell_with_data(data, min_pos=0):
            """Tell/seek to various points within a data stream and ensure
            that the decoded data returned by read() is consistent."""
            f = self.open(support.TESTFN, 'wb')
            f.write(data)
            f.close()
            f = self.open(support.TESTFN, encoding='test_decoder')
            f._CHUNK_SIZE = CHUNK_SIZE
            decoded = f.read()
            f.close()

            for i in range(min_pos, len(decoded) + 1): # seek positions
                for j in [1, 5, len(decoded) - i]: # read lengths
                    f = self.open(support.TESTFN, encoding='test_decoder')
                    self.assertEqual(f.read(i), decoded[:i])
                    cookie = f.tell()
                    self.assertEqual(f.read(j), decoded[i:i + j])
                    f.seek(cookie)
                    self.assertEqual(f.read(), decoded[i:])
                    f.close()

        # Enable the test decoder.
        StatefulIncrementalDecoder.codecEnabled = 1

        # Run the tests.
        try:
            # Try each test case.
            for input, _, _ in StatefulIncrementalDecoderTest.test_cases:
                test_seek_and_tell_with_data(input)

            # Position each test case so that it crosses a chunk boundary.
            for input, _, _ in StatefulIncrementalDecoderTest.test_cases:
                offset = CHUNK_SIZE - len(input)//2
                prefix = b'.'*offset
                # Don't bother seeking into the prefix (takes too long).
                min_pos = offset*2
                test_seek_and_tell_with_data(prefix + input, min_pos)

        # Ensure our test decoder won't interfere with subsequent tests.
        finally:
            StatefulIncrementalDecoder.codecEnabled = 0

    def test_encoded_writes(self):
        data = "1234567890"
        tests = ("utf-16",
                 "utf-16-le",
                 "utf-16-be",
                 "utf-32",
                 "utf-32-le",
                 "utf-32-be")
        for encoding in tests:
            buf = self.BytesIO()
            f = self.TextIOWrapper(buf, encoding=encoding)
            # Check if the BOM is written only once (see issue1753).
            f.write(data)
            f.write(data)
            f.seek(0)
            self.assertEqual(f.read(), data * 2)
            f.seek(0)
            self.assertEqual(f.read(), data * 2)
            self.assertEqual(buf.getvalue(), (data * 2).encode(encoding))

    def test_unreadable(self):
        class UnReadable(self.BytesIO):
            def readable(self):
                return False
        txt = self.TextIOWrapper(UnReadable())
        self.assertRaises(IOError, txt.read)

    def test_read_one_by_one(self):
        txt = self.TextIOWrapper(self.BytesIO(b"AA\r\nBB"))
        reads = ""
        while True:
            c = txt.read(1)
            if not c:
                break
            reads += c
        self.assertEqual(reads, "AA\nBB")

    def test_readlines(self):
        txt = self.TextIOWrapper(self.BytesIO(b"AA\nBB\nCC"))
        self.assertEqual(txt.readlines(), ["AA\n", "BB\n", "CC"])
        txt.seek(0)
        self.assertEqual(txt.readlines(None), ["AA\n", "BB\n", "CC"])
        txt.seek(0)
        self.assertEqual(txt.readlines(5), ["AA\n", "BB\n"])

    # read in amounts equal to TextIOWrapper._CHUNK_SIZE which is 128.
    def test_read_by_chunk(self):
        # make sure "\r\n" straddles 128 char boundary.
        txt = self.TextIOWrapper(self.BytesIO(b"A" * 127 + b"\r\nB"))
        reads = ""
        while True:
            c = txt.read(128)
            if not c:
                break
            reads += c
        self.assertEqual(reads, "A"*127+"\nB")

    def test_writelines(self):
        l = ['ab', 'cd', 'ef']
        buf = self.BytesIO()
        txt = self.TextIOWrapper(buf)
        txt.writelines(l)
        txt.flush()
        self.assertEqual(buf.getvalue(), b'abcdef')

    def test_writelines_userlist(self):
        l = UserList(['ab', 'cd', 'ef'])
        buf = self.BytesIO()
        txt = self.TextIOWrapper(buf)
        txt.writelines(l)
        txt.flush()
        self.assertEqual(buf.getvalue(), b'abcdef')

    def test_writelines_error(self):
        txt = self.TextIOWrapper(self.BytesIO())
        self.assertRaises(TypeError, txt.writelines, [1, 2, 3])
        self.assertRaises(TypeError, txt.writelines, None)
        self.assertRaises(TypeError, txt.writelines, b'abc')

    def test_issue1395_1(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")

        # read one char at a time
        reads = ""
        while True:
            c = txt.read(1)
            if not c:
                break
            reads += c
        self.assertEqual(reads, self.normalized)

    def test_issue1395_2(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        txt._CHUNK_SIZE = 4

        reads = ""
        while True:
            c = txt.read(4)
            if not c:
                break
            reads += c
        self.assertEqual(reads, self.normalized)

    def test_issue1395_3(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        txt._CHUNK_SIZE = 4

        reads = txt.read(4)
        reads += txt.read(4)
        reads += txt.readline()
        reads += txt.readline()
        reads += txt.readline()
        self.assertEqual(reads, self.normalized)

    def test_issue1395_4(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        txt._CHUNK_SIZE = 4

        reads = txt.read(4)
        reads += txt.read()
        self.assertEqual(reads, self.normalized)

    def test_issue1395_5(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        txt._CHUNK_SIZE = 4

        reads = txt.read(4)
        pos = txt.tell()
        txt.seek(0)
        txt.seek(pos)
        self.assertEqual(txt.read(4), "BBB\n")

    def test_issue2282(self):
        buffer = self.BytesIO(self.testdata)
        txt = self.TextIOWrapper(buffer, encoding="ascii")

        self.assertEqual(buffer.seekable(), txt.seekable())

    def test_append_bom(self):
        # The BOM is not written again when appending to a non-empty file
        filename = support.TESTFN
        for charset in ('utf-8-sig', 'utf-16', 'utf-32'):
            with self.open(filename, 'w', encoding=charset) as f:
                f.write('aaa')
                pos = f.tell()
            with self.open(filename, 'rb') as f:
                self.assertEqual(f.read(), 'aaa'.encode(charset))

            with self.open(filename, 'a', encoding=charset) as f:
                f.write('xxx')
            with self.open(filename, 'rb') as f:
                self.assertEqual(f.read(), 'aaaxxx'.encode(charset))

    def test_seek_bom(self):
        # Same test, but when seeking manually
        filename = support.TESTFN
        for charset in ('utf-8-sig', 'utf-16', 'utf-32'):
            with self.open(filename, 'w', encoding=charset) as f:
                f.write('aaa')
                pos = f.tell()
            with self.open(filename, 'r+', encoding=charset) as f:
                f.seek(pos)
                f.write('zzz')
                f.seek(0)
                f.write('bbb')
            with self.open(filename, 'rb') as f:
                self.assertEqual(f.read(), 'bbbzzz'.encode(charset))

    def test_errors_property(self):
        with self.open(support.TESTFN, "w") as f:
            self.assertEqual(f.errors, "strict")
        with self.open(support.TESTFN, "w", errors="replace") as f:
            self.assertEqual(f.errors, "replace")

    @unittest.skipUnless(threading, 'Threading required for this test.')
    def test_threads_write(self):
        # Issue6750: concurrent writes could duplicate data
        event = threading.Event()
        with self.open(support.TESTFN, "w", buffering=1) as f:
            def run(n):
                text = "Thread%03d\n" % n
                event.wait()
                f.write(text)
            threads = [threading.Thread(target=lambda n=x: run(n))
                       for x in range(20)]
            for t in threads:
                t.start()
            time.sleep(0.02)
            event.set()
            for t in threads:
                t.join()
        with self.open(support.TESTFN) as f:
            content = f.read()
            for n in range(20):
                self.assertEqual(content.count("Thread%03d\n" % n), 1)

    def test_flush_error_on_close(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        def bad_flush():
            raise IOError()
        txt.flush = bad_flush
        self.assertRaises(IOError, txt.close) # exception not swallowed
        self.assertTrue(txt.closed)

    def test_multi_close(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        txt.close()
        txt.close()
        txt.close()
        self.assertRaises(ValueError, txt.flush)

    def test_readonly_attributes(self):
        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
        buf = self.BytesIO(self.testdata)
        with self.assertRaises((AttributeError, TypeError)):
            txt.buffer = buf

    def test_read_nonbytes(self):
        # Issue #17106
        # Crash when underlying read() returns non-bytes
        class NonbytesStream(self.StringIO):
            read1 = self.StringIO.read
        class NonbytesStream(self.StringIO):
            read1 = self.StringIO.read
        t = self.TextIOWrapper(NonbytesStream('a'))
        with self.maybeRaises(TypeError):
            t.read(1)
        t = self.TextIOWrapper(NonbytesStream('a'))
        with self.maybeRaises(TypeError):
            t.readline()
        t = self.TextIOWrapper(NonbytesStream('a'))
        self.assertEqual(t.read(), u'a')

    def test_illegal_decoder(self):
        # Issue #17106
        # Crash when decoder returns non-string
        t = self.TextIOWrapper(self.BytesIO(b'aaaaaa'), newline='\n',
                               encoding='quopri_codec')
        with self.maybeRaises(TypeError):
            t.read(1)
        t = self.TextIOWrapper(self.BytesIO(b'aaaaaa'), newline='\n',
                               encoding='quopri_codec')
        with self.maybeRaises(TypeError):
            t.readline()
        t = self.TextIOWrapper(self.BytesIO(b'aaaaaa'), newline='\n',
                               encoding='quopri_codec')
        with self.maybeRaises(TypeError):
            t.read()


class CTextIOWrapperTest(TextIOWrapperTest):

    def test_initialization(self):
        r = self.BytesIO(b"\xc3\xa9\n\n")
        b = self.BufferedReader(r, 1000)
        t = self.TextIOWrapper(b)
        self.assertRaises(TypeError, t.__init__, b, newline=42)
        self.assertRaises(ValueError, t.read)
        self.assertRaises(ValueError, t.__init__, b, newline='xyzzy')
        self.assertRaises(ValueError, t.read)

    def test_garbage_collection(self):
        # C TextIOWrapper objects are collected, and collecting them flushes
        # all data to disk.
        # The Python version has __del__, so it ends in gc.garbage instead.
        rawio = io.FileIO(support.TESTFN, "wb")
        b = self.BufferedWriter(rawio)
        t = self.TextIOWrapper(b, encoding="ascii")
        t.write("456def")
        t.x = t
        wr = weakref.ref(t)
        del t
        support.gc_collect()
        self.assertTrue(wr() is None, wr)
        with self.open(support.TESTFN, "rb") as f:
            self.assertEqual(f.read(), b"456def")

    def test_rwpair_cleared_before_textio(self):
        # Issue 13070: TextIOWrapper's finalization would crash when called
        # after the reference to the underlying BufferedRWPair's writer got
        # cleared by the GC.
        for i in range(1000):
            b1 = self.BufferedRWPair(self.MockRawIO(), self.MockRawIO())
            t1 = self.TextIOWrapper(b1, encoding="ascii")
            b2 = self.BufferedRWPair(self.MockRawIO(), self.MockRawIO())
            t2 = self.TextIOWrapper(b2, encoding="ascii")
            # circular references
            t1.buddy = t2
            t2.buddy = t1
        support.gc_collect()

    maybeRaises = unittest.TestCase.assertRaises


class PyTextIOWrapperTest(TextIOWrapperTest):
    @contextlib.contextmanager
    def maybeRaises(self, *args, **kwds):
        yield


class IncrementalNewlineDecoderTest(unittest.TestCase):

    def check_newline_decoding_utf8(self, decoder):
        # UTF-8 specific tests for a newline decoder
        def _check_decode(b, s, **kwargs):
            # We exercise getstate() / setstate() as well as decode()
            state = decoder.getstate()
            self.assertEqual(decoder.decode(b, **kwargs), s)
            decoder.setstate(state)
            self.assertEqual(decoder.decode(b, **kwargs), s)

        _check_decode(b'\xe8\xa2\x88', "\u8888")

        _check_decode(b'\xe8', "")
        _check_decode(b'\xa2', "")
        _check_decode(b'\x88', "\u8888")

        _check_decode(b'\xe8', "")
        _check_decode(b'\xa2', "")
        _check_decode(b'\x88', "\u8888")

        _check_decode(b'\xe8', "")
        self.assertRaises(UnicodeDecodeError, decoder.decode, b'', final=True)

        decoder.reset()
        _check_decode(b'\n', "\n")
        _check_decode(b'\r', "")
        _check_decode(b'', "\n", final=True)
        _check_decode(b'\r', "\n", final=True)

        _check_decode(b'\r', "")
        _check_decode(b'a', "\na")

        _check_decode(b'\r\r\n', "\n\n")
        _check_decode(b'\r', "")
        _check_decode(b'\r', "\n")
        _check_decode(b'\na', "\na")

        _check_decode(b'\xe8\xa2\x88\r\n', "\u8888\n")
        _check_decode(b'\xe8\xa2\x88', "\u8888")
        _check_decode(b'\n', "\n")
        _check_decode(b'\xe8\xa2\x88\r', "\u8888")
        _check_decode(b'\n', "\n")

    def check_newline_decoding(self, decoder, encoding):
        result = []
        if encoding is not None:
            encoder = codecs.getincrementalencoder(encoding)()
            def _decode_bytewise(s):
                # Decode one byte at a time
                for b in encoder.encode(s):
                    result.append(decoder.decode(b))
        else:
            encoder = None
            def _decode_bytewise(s):
                # Decode one char at a time
                for c in s:
                    result.append(decoder.decode(c))
        self.assertEqual(decoder.newlines, None)
        _decode_bytewise("abc\n\r")
        self.assertEqual(decoder.newlines, '\n')
        _decode_bytewise("\nabc")
        self.assertEqual(decoder.newlines, ('\n', '\r\n'))
        _decode_bytewise("abc\r")
        self.assertEqual(decoder.newlines, ('\n', '\r\n'))
        _decode_bytewise("abc")
        self.assertEqual(decoder.newlines, ('\r', '\n', '\r\n'))
        _decode_bytewise("abc\r")
        self.assertEqual("".join(result), "abc\n\nabcabc\nabcabc")
        decoder.reset()
        input = "abc"
        if encoder is not None:
            encoder.reset()
            input = encoder.encode(input)
        self.assertEqual(decoder.decode(input), "abc")
        self.assertEqual(decoder.newlines, None)

    def test_newline_decoder(self):
        encodings = (
            # None meaning the IncrementalNewlineDecoder takes unicode input
            # rather than bytes input
            None, 'utf-8', 'latin-1',
            'utf-16', 'utf-16-le', 'utf-16-be',
            'utf-32', 'utf-32-le', 'utf-32-be',
        )
        for enc in encodings:
            decoder = enc and codecs.getincrementaldecoder(enc)()
            decoder = self.IncrementalNewlineDecoder(decoder, translate=True)
            self.check_newline_decoding(decoder, enc)
        decoder = codecs.getincrementaldecoder("utf-8")()
        decoder = self.IncrementalNewlineDecoder(decoder, translate=True)
        self.check_newline_decoding_utf8(decoder)

    def test_newline_bytes(self):
        # Issue 5433: Excessive optimization in IncrementalNewlineDecoder
        def _check(dec):
            self.assertEqual(dec.newlines, None)
            self.assertEqual(dec.decode("\u0D00"), "\u0D00")
            self.assertEqual(dec.newlines, None)
            self.assertEqual(dec.decode("\u0A00"), "\u0A00")
            self.assertEqual(dec.newlines, None)
        dec = self.IncrementalNewlineDecoder(None, translate=False)
        _check(dec)
        dec = self.IncrementalNewlineDecoder(None, translate=True)
        _check(dec)

class CIncrementalNewlineDecoderTest(IncrementalNewlineDecoderTest):
    pass

class PyIncrementalNewlineDecoderTest(IncrementalNewlineDecoderTest):
    pass


# XXX Tests for open()

class MiscIOTest(unittest.TestCase):

    def tearDown(self):
        support.unlink(support.TESTFN)

    def test___all__(self):
        for name in self.io.__all__:
            obj = getattr(self.io, name, None)
            self.assertTrue(obj is not None, name)
            if name == "open":
                continue
            elif "error" in name.lower() or name == "UnsupportedOperation":
                self.assertTrue(issubclass(obj, Exception), name)
            elif not name.startswith("SEEK_"):
                self.assertTrue(issubclass(obj, self.IOBase))

    def test_attributes(self):
        f = self.open(support.TESTFN, "wb", buffering=0)
        self.assertEqual(f.mode, "wb")
        f.close()

        f = self.open(support.TESTFN, "U")
        self.assertEqual(f.name,            support.TESTFN)
        self.assertEqual(f.buffer.name,     support.TESTFN)
        self.assertEqual(f.buffer.raw.name, support.TESTFN)
        self.assertEqual(f.mode,            "U")
        self.assertEqual(f.buffer.mode,     "rb")
        self.assertEqual(f.buffer.raw.mode, "rb")
        f.close()

        f = self.open(support.TESTFN, "w+")
        self.assertEqual(f.mode,            "w+")
        self.assertEqual(f.buffer.mode,     "rb+") # Does it really matter?
        self.assertEqual(f.buffer.raw.mode, "rb+")

        g = self.open(f.fileno(), "wb", closefd=False)
        self.assertEqual(g.mode,     "wb")
        self.assertEqual(g.raw.mode, "wb")
        self.assertEqual(g.name,     f.fileno())
        self.assertEqual(g.raw.name, f.fileno())
        f.close()
        g.close()

    def test_io_after_close(self):
        for kwargs in [
                {"mode": "w"},
                {"mode": "wb"},
                {"mode": "w", "buffering": 1},
                {"mode": "w", "buffering": 2},
                {"mode": "wb", "buffering": 0},
                {"mode": "r"},
                {"mode": "rb"},
                {"mode": "r", "buffering": 1},
                {"mode": "r", "buffering": 2},
                {"mode": "rb", "buffering": 0},
                {"mode": "w+"},
                {"mode": "w+b"},
                {"mode": "w+", "buffering": 1},
                {"mode": "w+", "buffering": 2},
                {"mode": "w+b", "buffering": 0},
            ]:
            f = self.open(support.TESTFN, **kwargs)
            f.close()
            self.assertRaises(ValueError, f.flush)
            self.assertRaises(ValueError, f.fileno)
            self.assertRaises(ValueError, f.isatty)
            self.assertRaises(ValueError, f.__iter__)
            if hasattr(f, "peek"):
                self.assertRaises(ValueError, f.peek, 1)
            self.assertRaises(ValueError, f.read)
            if hasattr(f, "read1"):
                self.assertRaises(ValueError, f.read1, 1024)
            if hasattr(f, "readall"):
                self.assertRaises(ValueError, f.readall)
            if hasattr(f, "readinto"):
                self.assertRaises(ValueError, f.readinto, bytearray(1024))
            self.assertRaises(ValueError, f.readline)
            self.assertRaises(ValueError, f.readlines)
            self.assertRaises(ValueError, f.seek, 0)
            self.assertRaises(ValueError, f.tell)
            self.assertRaises(ValueError, f.truncate)
            self.assertRaises(ValueError, f.write,
                              b"" if "b" in kwargs['mode'] else "")
            self.assertRaises(ValueError, f.writelines, [])
            self.assertRaises(ValueError, next, f)

    def test_blockingioerror(self):
        # Various BlockingIOError issues
        self.assertRaises(TypeError, self.BlockingIOError)
        self.assertRaises(TypeError, self.BlockingIOError, 1)
        self.assertRaises(TypeError, self.BlockingIOError, 1, 2, 3, 4)
        self.assertRaises(TypeError, self.BlockingIOError, 1, "", None)
        b = self.BlockingIOError(1, "")
        self.assertEqual(b.characters_written, 0)
        class C(unicode):
            pass
        c = C("")
        b = self.BlockingIOError(1, c)
        c.b = b
        b.c = c
        wr = weakref.ref(c)
        del c, b
        support.gc_collect()
        self.assertTrue(wr() is None, wr)

    def test_abcs(self):
        # Test the visible base classes are ABCs.
        self.assertIsInstance(self.IOBase, abc.ABCMeta)
        self.assertIsInstance(self.RawIOBase, abc.ABCMeta)
        self.assertIsInstance(self.BufferedIOBase, abc.ABCMeta)
        self.assertIsInstance(self.TextIOBase, abc.ABCMeta)

    def _check_abc_inheritance(self, abcmodule):
        with self.open(support.TESTFN, "wb", buffering=0) as f:
            self.assertIsInstance(f, abcmodule.IOBase)
            self.assertIsInstance(f, abcmodule.RawIOBase)
            self.assertNotIsInstance(f, abcmodule.BufferedIOBase)
            self.assertNotIsInstance(f, abcmodule.TextIOBase)
        with self.open(support.TESTFN, "wb") as f:
            self.assertIsInstance(f, abcmodule.IOBase)
            self.assertNotIsInstance(f, abcmodule.RawIOBase)
            self.assertIsInstance(f, abcmodule.BufferedIOBase)
            self.assertNotIsInstance(f, abcmodule.TextIOBase)
        with self.open(support.TESTFN, "w") as f:
            self.assertIsInstance(f, abcmodule.IOBase)
            self.assertNotIsInstance(f, abcmodule.RawIOBase)
            self.assertNotIsInstance(f, abcmodule.BufferedIOBase)
            self.assertIsInstance(f, abcmodule.TextIOBase)

    def test_abc_inheritance(self):
        # Test implementations inherit from their respective ABCs
        self._check_abc_inheritance(self)

    def test_abc_inheritance_official(self):
        # Test implementations inherit from the official ABCs of the
        # baseline "io" module.
        self._check_abc_inheritance(io)

    @unittest.skipUnless(fcntl, 'fcntl required for this test')
    def test_nonblock_pipe_write_bigbuf(self):
        self._test_nonblock_pipe_write(16*1024)

    @unittest.skipUnless(fcntl, 'fcntl required for this test')
    def test_nonblock_pipe_write_smallbuf(self):
        self._test_nonblock_pipe_write(1024)

    def _set_non_blocking(self, fd):
        flags = fcntl.fcntl(fd, fcntl.F_GETFL)
        self.assertNotEqual(flags, -1)
        res = fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
        self.assertEqual(res, 0)

    def _test_nonblock_pipe_write(self, bufsize):
        sent = []
        received = []
        r, w = os.pipe()
        self._set_non_blocking(r)
        self._set_non_blocking(w)

        # To exercise all code paths in the C implementation we need
        # to play with buffer sizes.  For instance, if we choose a
        # buffer size less than or equal to _PIPE_BUF (4096 on Linux)
        # then we will never get a partial write of the buffer.
        rf = self.open(r, mode='rb', closefd=True, buffering=bufsize)
        wf = self.open(w, mode='wb', closefd=True, buffering=bufsize)

        with rf, wf:
            for N in 9999, 73, 7574:
                try:
                    i = 0
                    while True:
                        msg = bytes([i % 26 + 97]) * N
                        sent.append(msg)
                        wf.write(msg)
                        i += 1

                except self.BlockingIOError as e:
                    self.assertEqual(e.args[0], errno.EAGAIN)
                    sent[-1] = sent[-1][:e.characters_written]
                    received.append(rf.read())
                    msg = b'BLOCKED'
                    wf.write(msg)
                    sent.append(msg)

            while True:
                try:
                    wf.flush()
                    break
                except self.BlockingIOError as e:
                    self.assertEqual(e.args[0], errno.EAGAIN)
                    self.assertEqual(e.characters_written, 0)
                    received.append(rf.read())

            received += iter(rf.read, None)

        sent, received = b''.join(sent), b''.join(received)
        self.assertTrue(sent == received)
        self.assertTrue(wf.closed)
        self.assertTrue(rf.closed)

class CMiscIOTest(MiscIOTest):
    io = io

class PyMiscIOTest(MiscIOTest):
    io = pyio


@unittest.skipIf(os.name == 'nt', 'POSIX signals required for this test.')
class SignalsTest(unittest.TestCase):

    def setUp(self):
        self.oldalrm = signal.signal(signal.SIGALRM, self.alarm_interrupt)

    def tearDown(self):
        signal.signal(signal.SIGALRM, self.oldalrm)

    def alarm_interrupt(self, sig, frame):
        1 // 0

    @unittest.skipUnless(threading, 'Threading required for this test.')
    @unittest.skipIf(sys.platform in ('freebsd5', 'freebsd6', 'freebsd7'),
                     'issue #12429: skip test on FreeBSD <= 7')
    def check_interrupted_write(self, item, bytes, **fdopen_kwargs):
        """Check that a partial write, when it gets interrupted, properly
        invokes the signal handler, and bubbles up the exception raised
        in the latter."""
        read_results = []
        def _read():
            s = os.read(r, 1)
            read_results.append(s)
        t = threading.Thread(target=_read)
        t.daemon = True
        r, w = os.pipe()
        try:
            wio = self.io.open(w, **fdopen_kwargs)
            t.start()
            signal.alarm(1)
            # Fill the pipe enough that the write will be blocking.
            # It will be interrupted by the timer armed above.  Since the
            # other thread has read one byte, the low-level write will
            # return with a successful (partial) result rather than an EINTR.
            # The buffered IO layer must check for pending signal
            # handlers, which in this case will invoke alarm_interrupt().
            self.assertRaises(ZeroDivisionError,
                        wio.write, item * (support.PIPE_MAX_SIZE // len(item) + 1))
            t.join()
            # We got one byte, get another one and check that it isn't a
            # repeat of the first one.
            read_results.append(os.read(r, 1))
            self.assertEqual(read_results, [bytes[0:1], bytes[1:2]])
        finally:
            os.close(w)
            os.close(r)
            # This is deliberate. If we didn't close the file descriptor
            # before closing wio, wio would try to flush its internal
            # buffer, and block again.
            try:
                wio.close()
            except IOError as e:
                if e.errno != errno.EBADF:
                    raise

    def test_interrupted_write_unbuffered(self):
        self.check_interrupted_write(b"xy", b"xy", mode="wb", buffering=0)

    def test_interrupted_write_buffered(self):
        self.check_interrupted_write(b"xy", b"xy", mode="wb")

    def test_interrupted_write_text(self):
        self.check_interrupted_write("xy", b"xy", mode="w", encoding="ascii")

    def check_reentrant_write(self, data, **fdopen_kwargs):
        def on_alarm(*args):
            # Will be called reentrantly from the same thread
            wio.write(data)
            1//0
        signal.signal(signal.SIGALRM, on_alarm)
        r, w = os.pipe()
        wio = self.io.open(w, **fdopen_kwargs)
        try:
            signal.alarm(1)
            # Either the reentrant call to wio.write() fails with RuntimeError,
            # or the signal handler raises ZeroDivisionError.
            with self.assertRaises((ZeroDivisionError, RuntimeError)) as cm:
                while 1:
                    for i in range(100):
                        wio.write(data)
                        wio.flush()
                    # Make sure the buffer doesn't fill up and block further writes
                    os.read(r, len(data) * 100)
            exc = cm.exception
            if isinstance(exc, RuntimeError):
                self.assertTrue(str(exc).startswith("reentrant call"), str(exc))
        finally:
            wio.close()
            os.close(r)

    def test_reentrant_write_buffered(self):
        self.check_reentrant_write(b"xy", mode="wb")

    def test_reentrant_write_text(self):
        self.check_reentrant_write("xy", mode="w", encoding="ascii")

    def check_interrupted_read_retry(self, decode, **fdopen_kwargs):
        """Check that a buffered read, when it gets interrupted (either
        returning a partial result or EINTR), properly invokes the signal
        handler and retries if the latter returned successfully."""
        r, w = os.pipe()
        fdopen_kwargs["closefd"] = False
        def alarm_handler(sig, frame):
            os.write(w, b"bar")
        signal.signal(signal.SIGALRM, alarm_handler)
        try:
            rio = self.io.open(r, **fdopen_kwargs)
            os.write(w, b"foo")
            signal.alarm(1)
            # Expected behaviour:
            # - first raw read() returns partial b"foo"
            # - second raw read() returns EINTR
            # - third raw read() returns b"bar"
            self.assertEqual(decode(rio.read(6)), "foobar")
        finally:
            rio.close()
            os.close(w)
            os.close(r)

    def test_interrupterd_read_retry_buffered(self):
        self.check_interrupted_read_retry(lambda x: x.decode('latin1'),
                                          mode="rb")

    def test_interrupterd_read_retry_text(self):
        self.check_interrupted_read_retry(lambda x: x,
                                          mode="r")

    @unittest.skipUnless(threading, 'Threading required for this test.')
    def check_interrupted_write_retry(self, item, **fdopen_kwargs):
        """Check that a buffered write, when it gets interrupted (either
        returning a partial result or EINTR), properly invokes the signal
        handler and retries if the latter returned successfully."""
        select = support.import_module("select")
        # A quantity that exceeds the buffer size of an anonymous pipe's
        # write end.
        N = support.PIPE_MAX_SIZE
        r, w = os.pipe()
        fdopen_kwargs["closefd"] = False
        # We need a separate thread to read from the pipe and allow the
        # write() to finish.  This thread is started after the SIGALRM is
        # received (forcing a first EINTR in write()).
        read_results = []
        write_finished = False
        def _read():
            while not write_finished:
                while r in select.select([r], [], [], 1.0)[0]:
                    s = os.read(r, 1024)
                    read_results.append(s)
        t = threading.Thread(target=_read)
        t.daemon = True
        def alarm1(sig, frame):
            signal.signal(signal.SIGALRM, alarm2)
            signal.alarm(1)
        def alarm2(sig, frame):
            t.start()
        signal.signal(signal.SIGALRM, alarm1)
        try:
            wio = self.io.open(w, **fdopen_kwargs)
            signal.alarm(1)
            # Expected behaviour:
            # - first raw write() is partial (because of the limited pipe buffer
            #   and the first alarm)
            # - second raw write() returns EINTR (because of the second alarm)
            # - subsequent write()s are successful (either partial or complete)
            self.assertEqual(N, wio.write(item * N))
            wio.flush()
            write_finished = True
            t.join()
            self.assertEqual(N, sum(len(x) for x in read_results))
        finally:
            write_finished = True
            os.close(w)
            os.close(r)
            # This is deliberate. If we didn't close the file descriptor
            # before closing wio, wio would try to flush its internal
            # buffer, and could block (in case of failure).
            try:
                wio.close()
            except IOError as e:
                if e.errno != errno.EBADF:
                    raise

    def test_interrupterd_write_retry_buffered(self):
        self.check_interrupted_write_retry(b"x", mode="wb")

    def test_interrupterd_write_retry_text(self):
        self.check_interrupted_write_retry("x", mode="w", encoding="latin1")


class CSignalsTest(SignalsTest):
    io = io

class PySignalsTest(SignalsTest):
    io = pyio

    # Handling reentrancy issues would slow down _pyio even more, so the
    # tests are disabled.
    test_reentrant_write_buffered = None
    test_reentrant_write_text = None


def test_main():
    tests = (CIOTest, PyIOTest,
             CBufferedReaderTest, PyBufferedReaderTest,
             CBufferedWriterTest, PyBufferedWriterTest,
             CBufferedRWPairTest, PyBufferedRWPairTest,
             CBufferedRandomTest, PyBufferedRandomTest,
             StatefulIncrementalDecoderTest,
             CIncrementalNewlineDecoderTest, PyIncrementalNewlineDecoderTest,
             CTextIOWrapperTest, PyTextIOWrapperTest,
             CMiscIOTest, PyMiscIOTest,
             CSignalsTest, PySignalsTest,
             )

    # Put the namespaces of the IO module we are testing and some useful mock
    # classes in the __dict__ of each test.
    mocks = (MockRawIO, MisbehavedRawIO, MockFileIO, CloseFailureIO,
             MockNonBlockWriterIO, MockRawIOWithoutRead)
    all_members = io.__all__ + ["IncrementalNewlineDecoder"]
    c_io_ns = dict((name, getattr(io, name)) for name in all_members)
    py_io_ns = dict((name, getattr(pyio, name)) for name in all_members)
    globs = globals()
    c_io_ns.update((x.__name__, globs["C" + x.__name__]) for x in mocks)
    py_io_ns.update((x.__name__, globs["Py" + x.__name__]) for x in mocks)
    # Avoid turning open into a bound method.
    py_io_ns["open"] = pyio.OpenWrapper
    for test in tests:
        if test.__name__.startswith("C"):
            for name, obj in c_io_ns.items():
                setattr(test, name, obj)
        elif test.__name__.startswith("Py"):
            for name, obj in py_io_ns.items():
                setattr(test, name, obj)

    support.run_unittest(*tests)

if __name__ == "__main__":
    test_main()