diff --git a/Lib/lib2to3/main.py b/Lib/lib2to3/main.py
index c092886..02e28e3 100644
--- a/Lib/lib2to3/main.py
+++ b/Lib/lib2to3/main.py
@@ -10,6 +10,20 @@
 from . import refactor
 
 
+class StdoutRefactoringTool(refactor.RefactoringTool):
+    """
+    Prints output to stdout.
+    """
+
+    def log_error(self, msg, *args, **kwargs):
+        self.errors.append((msg, args, kwargs))
+        self.logger.error(msg, *args, **kwargs)
+
+    def print_output(self, lines):
+        for line in lines:
+            print line
+
+
 def main(fixer_pkg, args=None):
     """Main program.
 
@@ -68,7 +82,7 @@
         fixer_names = avail_names if "all" in options.fix else explicit
     else:
         fixer_names = avail_names
-    rt = refactor.RefactoringTool(fixer_names, rt_opts, explicit=explicit)
+    rt = StdoutRefactoringTool(fixer_names, rt_opts, explicit=explicit)
 
     # Refactor all files and directories passed as arguments
     if not rt.errors:
@@ -80,7 +94,3 @@
 
     # Return error status (0 if rt.errors is zero)
     return int(bool(rt.errors))
-
-
-if __name__ == "__main__":
-    sys.exit(main())
diff --git a/Lib/lib2to3/refactor.py b/Lib/lib2to3/refactor.py
index 17304a8..aa97b82 100755
--- a/Lib/lib2to3/refactor.py
+++ b/Lib/lib2to3/refactor.py
@@ -90,11 +90,18 @@
             for fix_name in get_all_fix_names(pkg_name, False)]
 
 
+class FixerError(Exception):
+    """A fixer could not be loaded."""
+
+
 class RefactoringTool(object):
 
     _default_options = {"print_function": False}
 
-    def __init__(self, fixer_names, options=None, explicit=[]):
+    CLASS_PREFIX = "Fix" # The prefix for fixer classes
+    FILE_PREFIX = "fix_" # The prefix for modules with a fixer within
+
+    def __init__(self, fixer_names, options=None, explicit=None):
         """Initializer.
 
         Args:
@@ -103,7 +110,7 @@
             explicit: a list of fixers to run even if they are explicit.
         """
         self.fixers = fixer_names
-        self.explicit = explicit
+        self.explicit = explicit or []
         self.options = self._default_options.copy()
         if options is not None:
             self.options.update(options)
@@ -134,29 +141,17 @@
         pre_order_fixers = []
         post_order_fixers = []
         for fix_mod_path in self.fixers:
-            try:
-                mod = __import__(fix_mod_path, {}, {}, ["*"])
-            except ImportError:
-                self.log_error("Can't load transformation module %s",
-                               fix_mod_path)
-                continue
+            mod = __import__(fix_mod_path, {}, {}, ["*"])
             fix_name = fix_mod_path.rsplit(".", 1)[-1]
-            if fix_name.startswith("fix_"):
-                fix_name = fix_name[4:]
+            if fix_name.startswith(self.FILE_PREFIX):
+                fix_name = fix_name[len(self.FILE_PREFIX):]
             parts = fix_name.split("_")
-            class_name = "Fix" + "".join([p.title() for p in parts])
+            class_name = self.CLASS_PREFIX + "".join([p.title() for p in parts])
             try:
                 fix_class = getattr(mod, class_name)
             except AttributeError:
-                self.log_error("Can't find %s.%s",
-                               fix_name, class_name)
-                continue
-            try:
-                fixer = fix_class(self.options, self.fixer_log)
-            except Exception, err:
-                self.log_error("Can't instantiate fixes.fix_%s.%s()",
-                               fix_name, class_name, exc_info=True)
-                continue
+                raise FixerError("Can't find %s.%s" % (fix_name, class_name))
+            fixer = fix_class(self.options, self.fixer_log)
             if fixer.explicit and self.explicit is not True and \
                     fix_mod_path not in self.explicit:
                 self.log_message("Skipping implicit fixer: %s", fix_name)
@@ -168,7 +163,7 @@
             elif fixer.order == "post":
                 post_order_fixers.append(fixer)
             else:
-                raise ValueError("Illegal fixer order: %r" % fixer.order)
+                raise FixerError("Illegal fixer order: %r" % fixer.order)
 
         key_func = operator.attrgetter("run_order")
         pre_order_fixers.sort(key=key_func)
@@ -176,9 +171,8 @@
         return (pre_order_fixers, post_order_fixers)
 
     def log_error(self, msg, *args, **kwds):
-        """Increments error count and log a message."""
-        self.errors.append((msg, args, kwds))
-        self.logger.error(msg, *args, **kwds)
+        """Called when an error occurs."""
+        raise
 
     def log_message(self, msg, *args):
         """Hook to log a message."""
@@ -191,13 +185,17 @@
             msg = msg % args
         self.logger.debug(msg)
 
+    def print_output(self, lines):
+        """Called with lines of output to give to the user."""
+        pass
+
     def refactor(self, items, write=False, doctests_only=False):
         """Refactor a list of files and directories."""
         for dir_or_file in items:
             if os.path.isdir(dir_or_file):
-                self.refactor_dir(dir_or_file, write)
+                self.refactor_dir(dir_or_file, write, doctests_only)
             else:
-                self.refactor_file(dir_or_file, write)
+                self.refactor_file(dir_or_file, write, doctests_only)
 
     def refactor_dir(self, dir_name, write=False, doctests_only=False):
         """Descends down a directory and refactor every Python file found.
@@ -348,12 +346,11 @@
         if old_text == new_text:
             self.log_debug("No changes to %s", filename)
             return
-        diff_texts(old_text, new_text, filename)
-        if not write:
-            self.log_debug("Not writing changes to %s", filename)
-            return
+        self.print_output(diff_texts(old_text, new_text, filename))
         if write:
             self.write_file(new_text, filename, old_text)
+        else:
+            self.log_debug("Not writing changes to %s", filename)
 
     def write_file(self, new_text, filename, old_text=None):
         """Writes a string to a file.
@@ -528,10 +525,9 @@
 
 
 def diff_texts(a, b, filename):
-    """Prints a unified diff of two strings."""
+    """Return a unified diff of two strings."""
     a = a.splitlines()
     b = b.splitlines()
-    for line in difflib.unified_diff(a, b, filename, filename,
-                                     "(original)", "(refactored)",
-                                     lineterm=""):
-        print line
+    return difflib.unified_diff(a, b, filename, filename,
+                                "(original)", "(refactored)",
+                                lineterm="")
diff --git a/Lib/lib2to3/tests/data/fixers/bad_order.py b/Lib/lib2to3/tests/data/fixers/bad_order.py
new file mode 100644
index 0000000..061bbf2
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/bad_order.py
@@ -0,0 +1,5 @@
+from lib2to3.fixer_base import BaseFix
+
+class FixBadOrder(BaseFix):
+
+    order = "crazy"
diff --git a/Lib/lib2to3/tests/data/fixers/myfixes/__init__.py b/Lib/lib2to3/tests/data/fixers/myfixes/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/myfixes/__init__.py
diff --git a/Lib/lib2to3/tests/data/fixers/myfixes/fix_explicit.py b/Lib/lib2to3/tests/data/fixers/myfixes/fix_explicit.py
new file mode 100644
index 0000000..cbe16f6
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/myfixes/fix_explicit.py
@@ -0,0 +1,6 @@
+from lib2to3.fixer_base import BaseFix
+
+class FixExplicit(BaseFix):
+    explicit = True
+
+    def match(self): return False
diff --git a/Lib/lib2to3/tests/data/fixers/myfixes/fix_first.py b/Lib/lib2to3/tests/data/fixers/myfixes/fix_first.py
new file mode 100644
index 0000000..a88821f
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/myfixes/fix_first.py
@@ -0,0 +1,6 @@
+from lib2to3.fixer_base import BaseFix
+
+class FixFirst(BaseFix):
+    run_order = 1
+
+    def match(self, node): return False
diff --git a/Lib/lib2to3/tests/data/fixers/myfixes/fix_last.py b/Lib/lib2to3/tests/data/fixers/myfixes/fix_last.py
new file mode 100644
index 0000000..9a077d4
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/myfixes/fix_last.py
@@ -0,0 +1,7 @@
+from lib2to3.fixer_base import BaseFix
+
+class FixLast(BaseFix):
+
+    run_order = 10
+
+    def match(self, node): return False
diff --git a/Lib/lib2to3/tests/data/fixers/myfixes/fix_parrot.py b/Lib/lib2to3/tests/data/fixers/myfixes/fix_parrot.py
new file mode 100644
index 0000000..6bd2f49
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/myfixes/fix_parrot.py
@@ -0,0 +1,13 @@
+from lib2to3.fixer_base import BaseFix
+from lib2to3.fixer_util import Name
+
+class FixParrot(BaseFix):
+    """
+    Change functions named 'parrot' to 'cheese'.
+    """
+
+    PATTERN = """funcdef < 'def' name='parrot' any* >"""
+
+    def transform(self, node, results):
+        name = results["name"]
+        name.replace(Name("cheese", name.get_prefix()))
diff --git a/Lib/lib2to3/tests/data/fixers/myfixes/fix_preorder.py b/Lib/lib2to3/tests/data/fixers/myfixes/fix_preorder.py
new file mode 100644
index 0000000..b9bfbba
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/myfixes/fix_preorder.py
@@ -0,0 +1,6 @@
+from lib2to3.fixer_base import BaseFix
+
+class FixPreorder(BaseFix):
+    order = "pre"
+
+    def match(self, node): return False
diff --git a/Lib/lib2to3/tests/data/fixers/no_fixer_cls.py b/Lib/lib2to3/tests/data/fixers/no_fixer_cls.py
new file mode 100644
index 0000000..506f794
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/no_fixer_cls.py
@@ -0,0 +1 @@
+# This is empty so trying to fetch the fixer class gives an AttributeError
diff --git a/Lib/lib2to3/tests/data/fixers/parrot_example.py b/Lib/lib2to3/tests/data/fixers/parrot_example.py
new file mode 100644
index 0000000..0852928
--- /dev/null
+++ b/Lib/lib2to3/tests/data/fixers/parrot_example.py
@@ -0,0 +1,2 @@
+def parrot():
+    pass
diff --git a/Lib/lib2to3/tests/test_refactor.py b/Lib/lib2to3/tests/test_refactor.py
new file mode 100644
index 0000000..fac8f80
--- /dev/null
+++ b/Lib/lib2to3/tests/test_refactor.py
@@ -0,0 +1,175 @@
+"""
+Unit tests for refactor.py.
+"""
+
+import sys
+import os
+import operator
+import StringIO
+import tempfile
+import unittest
+
+from lib2to3 import refactor, pygram, fixer_base
+
+from . import support
+
+
+FIXER_DIR = os.path.join(os.path.dirname(__file__), "data/fixers")
+
+sys.path.append(FIXER_DIR)
+try:
+    _DEFAULT_FIXERS = refactor.get_fixers_from_package("myfixes")
+finally:
+    sys.path.pop()
+
+class TestRefactoringTool(unittest.TestCase):
+
+    def setUp(self):
+        sys.path.append(FIXER_DIR)
+
+    def tearDown(self):
+        sys.path.pop()
+
+    def check_instances(self, instances, classes):
+        for inst, cls in zip(instances, classes):
+            if not isinstance(inst, cls):
+                self.fail("%s are not instances of %s" % instances, classes)
+
+    def rt(self, options=None, fixers=_DEFAULT_FIXERS, explicit=None):
+        return refactor.RefactoringTool(fixers, options, explicit)
+
+    def test_print_function_option(self):
+        gram = pygram.python_grammar
+        save = gram.keywords["print"]
+        try:
+            rt = self.rt({"print_function" : True})
+            self.assertRaises(KeyError, operator.itemgetter("print"),
+                              gram.keywords)
+        finally:
+            gram.keywords["print"] = save
+
+    def test_fixer_loading_helpers(self):
+        contents = ["explicit", "first", "last", "parrot", "preorder"]
+        non_prefixed = refactor.get_all_fix_names("myfixes")
+        prefixed = refactor.get_all_fix_names("myfixes", False)
+        full_names = refactor.get_fixers_from_package("myfixes")
+        self.assertEqual(prefixed, ["fix_" + name for name in contents])
+        self.assertEqual(non_prefixed, contents)
+        self.assertEqual(full_names,
+                         ["myfixes.fix_" + name for name in contents])
+
+    def test_get_headnode_dict(self):
+        class NoneFix(fixer_base.BaseFix):
+            PATTERN = None
+
+        class FileInputFix(fixer_base.BaseFix):
+            PATTERN = "file_input< any * >"
+
+        no_head = NoneFix({}, [])
+        with_head = FileInputFix({}, [])
+        d = refactor.get_headnode_dict([no_head, with_head])
+        expected = {None: [no_head],
+                    pygram.python_symbols.file_input : [with_head]}
+        self.assertEqual(d, expected)
+
+    def test_fixer_loading(self):
+        from myfixes.fix_first import FixFirst
+        from myfixes.fix_last import FixLast
+        from myfixes.fix_parrot import FixParrot
+        from myfixes.fix_preorder import FixPreorder
+
+        rt = self.rt()
+        pre, post = rt.get_fixers()
+
+        self.check_instances(pre, [FixPreorder])
+        self.check_instances(post, [FixFirst, FixParrot, FixLast])
+
+    def test_naughty_fixers(self):
+        self.assertRaises(ImportError, self.rt, fixers=["not_here"])
+        self.assertRaises(refactor.FixerError, self.rt, fixers=["no_fixer_cls"])
+        self.assertRaises(refactor.FixerError, self.rt, fixers=["bad_order"])
+
+    def test_refactor_string(self):
+        rt = self.rt()
+        input = "def parrot(): pass\n\n"
+        tree = rt.refactor_string(input, "<test>")
+        self.assertNotEqual(str(tree), input)
+
+        input = "def f(): pass\n\n"
+        tree = rt.refactor_string(input, "<test>")
+        self.assertEqual(str(tree), input)
+
+    def test_refactor_stdin(self):
+
+        class MyRT(refactor.RefactoringTool):
+
+            def print_output(self, lines):
+                diff_lines.extend(lines)
+
+        diff_lines = []
+        rt = MyRT(_DEFAULT_FIXERS)
+        save = sys.stdin
+        sys.stdin = StringIO.StringIO("def parrot(): pass\n\n")
+        try:
+            rt.refactor_stdin()
+        finally:
+            sys.stdin = save
+        expected = """--- <stdin> (original)
++++ <stdin> (refactored)
+@@ -1,2 +1,2 @@
+-def parrot(): pass
++def cheese(): pass""".splitlines()
+        self.assertEqual(diff_lines[:-1], expected)
+
+    def test_refactor_file(self):
+        test_file = os.path.join(FIXER_DIR, "parrot_example.py")
+        backup = test_file + ".bak"
+        old_contents = open(test_file, "r").read()
+        rt = self.rt()
+
+        rt.refactor_file(test_file)
+        self.assertEqual(old_contents, open(test_file, "r").read())
+
+        rt.refactor_file(test_file, True)
+        try:
+            self.assertNotEqual(old_contents, open(test_file, "r").read())
+            self.assertTrue(os.path.exists(backup))
+            self.assertEqual(old_contents, open(backup, "r").read())
+        finally:
+            open(test_file, "w").write(old_contents)
+            try:
+                os.unlink(backup)
+            except OSError:
+                pass
+
+    def test_refactor_docstring(self):
+        rt = self.rt()
+
+        def example():
+            """
+            >>> example()
+            42
+            """
+        out = rt.refactor_docstring(example.__doc__, "<test>")
+        self.assertEqual(out, example.__doc__)
+
+        def parrot():
+            """
+            >>> def parrot():
+            ...      return 43
+            """
+        out = rt.refactor_docstring(parrot.__doc__, "<test>")
+        self.assertNotEqual(out, parrot.__doc__)
+
+    def test_explicit(self):
+        from myfixes.fix_explicit import FixExplicit
+
+        rt = self.rt(fixers=["myfixes.fix_explicit"])
+        self.assertEqual(len(rt.post_order), 0)
+
+        rt = self.rt(explicit=["myfixes.fix_explicit"])
+        for fix in rt.post_order[None]:
+            if isinstance(fix, FixExplicit):
+                break
+        else:
+            self.fail("explicit fixer not loaded")