diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 8960ce9..c58548e 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -828,7 +828,7 @@
         if self.closed:
             raise ValueError("seek on closed file")
         try:
-            pos = pos.__index__()
+            pos.__index__
         except AttributeError as err:
             raise TypeError("an integer is required") from err
         if whence == 0:
@@ -853,8 +853,13 @@
             raise ValueError("truncate on closed file")
         if pos is None:
             pos = self._pos
-        elif pos < 0:
-            raise ValueError("negative truncate position %r" % (pos,))
+        else:
+            try:
+                pos.__index__
+            except AttributeError as err:
+                raise TypeError("an integer is required") from err
+            if pos < 0:
+                raise ValueError("negative truncate position %r" % (pos,))
         del self._buffer[pos:]
         return pos
 
@@ -1803,6 +1808,10 @@
         if n is None:
             n = -1
         decoder = self._decoder or self._get_decoder()
+        try:
+            n.__index__
+        except AttributeError as err:
+            raise TypeError("an integer is required") from err
         if n < 0:
             # Read everything.
             result = (self._get_decoded_chars() +
diff --git a/Lib/test/support.py b/Lib/test/support.py
index bf49bab..769f94a 100644
--- a/Lib/test/support.py
+++ b/Lib/test/support.py
@@ -16,6 +16,7 @@
 import unittest
 import importlib
 import collections
+import re
 
 __all__ = ["Error", "TestFailed", "ResourceDenied", "import_module",
            "verbose", "use_resources", "max_memuse", "record_original_stdout",
@@ -464,22 +465,80 @@
        entry to the warnings.catch_warnings() context manager.
     """
     def __init__(self, warnings_list):
-        self.warnings = warnings_list
+        self._warnings = warnings_list
+        self._last = 0
 
     def __getattr__(self, attr):
-        if self.warnings:
-            return getattr(self.warnings[-1], attr)
+        if len(self._warnings) > self._last:
+            return getattr(self._warnings[-1], attr)
         elif attr in warnings.WarningMessage._WARNING_DETAILS:
             return None
         raise AttributeError("%r has no attribute %r" % (self, attr))
 
+    @property
+    def warnings(self):
+        return self._warnings[self._last:]
+
     def reset(self):
-        del self.warnings[:]
+        self._last = len(self._warnings)
+
+
+def _filterwarnings(filters, quiet=False):
+    """Catch the warnings, then check if all the expected
+    warnings have been raised and re-raise unexpected warnings.
+    If 'quiet' is True, only re-raise the unexpected warnings.
+    """
+    # Clear the warning registry of the calling module
+    # in order to re-raise the warnings.
+    frame = sys._getframe(2)
+    registry = frame.f_globals.get('__warningregistry__')
+    if registry:
+        registry.clear()
+    with warnings.catch_warnings(record=True) as w:
+        # Set filter "always" to record all warnings.  Because
+        # test_warnings swap the module, we need to look up in
+        # the sys.modules dictionary.
+        sys.modules['warnings'].simplefilter("always")
+        yield WarningsRecorder(w)
+    # Filter the recorded warnings
+    reraise = [warning.message for warning in w]
+    missing = []
+    for msg, cat in filters:
+        seen = False
+        for exc in reraise[:]:
+            message = str(exc)
+            # Filter out the matching messages
+            if (re.match(msg, message, re.I) and
+                issubclass(exc.__class__, cat)):
+                seen = True
+                reraise.remove(exc)
+        if not seen and not quiet:
+            # This filter caught nothing
+            missing.append((msg, cat.__name__))
+    if reraise:
+        raise AssertionError("unhandled warning %r" % reraise[0])
+    if missing:
+        raise AssertionError("filter (%r, %s) did not catch any warning" %
+                             missing[0])
+
 
 @contextlib.contextmanager
-def check_warnings():
-    with warnings.catch_warnings(record=True) as w:
-        yield WarningsRecorder(w)
+def check_warnings(*filters, **kwargs):
+    """Context manager to silence warnings.
+
+    Accept 2-tuples as positional arguments:
+        ("message regexp", WarningCategory)
+
+    Optional argument:
+     - if 'quiet' is True, it does not fail if a filter catches nothing
+        (default False)
+
+    Without argument, it defaults to:
+        check_warnings(("", Warning), quiet=False)
+    """
+    if not filters:
+        filters = (("", Warning),)
+    return _filterwarnings(filters, kwargs.get('quiet'))
 
 
 class CleanImport(object):
@@ -714,7 +773,6 @@
 MAX_Py_ssize_t = sys.maxsize
 
 def set_memlimit(limit):
-    import re
     global max_memuse
     global real_max_memuse
     sizes = {
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index 8348f6e..fd27512 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -390,7 +390,7 @@
         self.assertRaises(TypeError, _FileIO, "1", 0, 0)
 
     def testWarnings(self):
-        with check_warnings() as w:
+        with check_warnings(quiet=True) as w:
             self.assertEqual(w.warnings, [])
             self.assertRaises(TypeError, _FileIO, [])
             self.assertEqual(w.warnings, [])