Rebase on Python 3.5 contextlib

contextlib2.py

@@ -1,30 +1,19 @@
 """contextlib2 - backports and enhancements to the contextlib module"""
 
 import sys
+import warnings
 from collections import deque
 from functools import wraps
 
-# Standard library exports
 __all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack",
-           "redirect_stdout", "suppress"]
+           "redirect_stdout", "redirect_stderr", "suppress"]
 
-# contextlib2 only exports (current and legacy experimental interfaces)
+# Backwards compatibility
 __all__ += ["ContextStack"]
 
 class ContextDecorator(object):
     "A base class or mixin that enables context managers to work as decorators."
 
-    def _recreate_cm(self):
-        """Return a recreated instance of self.
-        Allows an otherwise one-shot context manager like
-        _GeneratorContextManager to support use as
-        a decorator via implicit recreation.
-
-        This is a private interface just for _GeneratorContextManager.
-        See issue #11647 for details.
-        """
-        return self
-
     def refresh_cm(self):
         """Returns the context manager used to actually wrap the call to the
         decorated function.
@@ -34,13 +23,30 @@ class ContextDecorator(object):
         Overriding this method allows otherwise one-shot context managers
         like _GeneratorContextManager to support use as decorators via
         implicit recreation.
+
+        DEPRECATED: refresh_cm was never added to the standard library's
+                    ContextDecorator API
+        """
+        warnings.warn("refresh_cm was never added to the standard library",
+                      DeprecationWarning)
+        return self._recreate_cm()
+
+    def _recreate_cm(self):
+        """Return a recreated instance of self.
+
+        Allows an otherwise one-shot context manager like
+        _GeneratorContextManager to support use as
+        a decorator via implicit recreation.
+
+        This is a private interface just for _GeneratorContextManager.
+        See issue #11647 for details.
         """
         return self
 
     def __call__(self, func):
         @wraps(func)
         def inner(*args, **kwds):
-            with self.refresh_cm():
+            with self._recreate_cm():
                 return func(*args, **kwds)
         return inner
 
@@ -48,7 +54,7 @@ class ContextDecorator(object):
 class _GeneratorContextManager(ContextDecorator):
     """Helper for @contextmanager decorator."""
 
-    def __init__(self, func, *args, **kwds):
+    def __init__(self, func, args, kwds):
         self.gen = func(*args, **kwds)
         self.func, self.args, self.kwds = func, args, kwds
         # Issue 19330: ensure context manager instances have good docstrings
@@ -62,11 +68,11 @@ class _GeneratorContextManager(ContextDecorator):
         # for the class instead.
         # See http://bugs.python.org/issue19404 for more details.
 
-    def refresh_cm(self):
+    def _recreate_cm(self):
         # _GCM instances are one-shot context managers, so the
         # CM must be recreated each time a decorated function is
         # called
-        return self.__class__(self.func, *self.args, **self.kwds)
+        return self.__class__(self.func, self.args, self.kwds)
 
     def __enter__(self):
         try:
@@ -91,10 +97,17 @@ class _GeneratorContextManager(ContextDecorator):
                 self.gen.throw(type, value, traceback)
                 raise RuntimeError("generator didn't stop after throw()")
             except StopIteration as exc:
-                # Suppress the exception *unless* it's the same exception that
+                # Suppress StopIteration *unless* it's the same exception that
                 # was passed to throw().  This prevents a StopIteration
-                # raised inside the "with" statement from being suppressed
+                # raised inside the "with" statement from being suppressed.
                 return exc is not value
+            except RuntimeError as exc:
+                # Likewise, avoid suppressing if a StopIteration exception
+                # was passed to throw() and later wrapped into a RuntimeError
+                # (see PEP 479).
+                if _HAVE_EXCEPTION_CHAINING and exc.__cause__ is value:
+                    return False
+                raise
             except:
                 # only re-raise if it's *not* the exception that was
                 # passed to throw(), because __exit__() must not raise
@@ -137,7 +150,7 @@ def contextmanager(func):
     """
     @wraps(func)
     def helper(*args, **kwds):
-        return _GeneratorContextManager(func, *args, **kwds)
+        return _GeneratorContextManager(func, args, kwds)
     return helper
 
 
@@ -165,8 +178,27 @@ class closing(object):
     def __exit__(self, *exc_info):
         self.thing.close()
 
-class redirect_stdout:
-    """Context manager for temporarily redirecting stdout to another file
+
+class _RedirectStream:
+
+    _stream = None
+
+    def __init__(self, new_target):
+        self._new_target = new_target
+        # We use a list of old targets to make this CM re-entrant
+        self._old_targets = []
+
+    def __enter__(self):
+        self._old_targets.append(getattr(sys, self._stream))
+        setattr(sys, self._stream, self._new_target)
+        return self._new_target
+
+    def __exit__(self, exctype, excinst, exctb):
+        setattr(sys, self._stream, self._old_targets.pop())
+
+
+class redirect_stdout(_RedirectStream):
+    """Context manager for temporarily redirecting stdout to another file.
 
         # How to send help() to stderr
         with redirect_stdout(sys.stderr):
@@ -178,22 +210,13 @@ class redirect_stdout:
                 help(pow)
     """
 
-    def __init__(self, new_target):
-        self._new_target = new_target
-        self._old_target = self._sentinel = object()
+    _stream = "stdout"
 
-    def __enter__(self):
-        if self._old_target is not self._sentinel:
-            raise RuntimeError("Cannot reenter {0!r}".format(self))
-        self._old_target = sys.stdout
-        sys.stdout = self._new_target
-        return self._new_target
 
-    def __exit__(self, exctype, excinst, exctb):
-        restore_stdout = self._old_target
-        self._old_target = self._sentinel
-        sys.stdout = restore_stdout
+class redirect_stderr(_RedirectStream):
+    """Context manager for temporarily redirecting stderr to another file."""
 
+    _stream = "stderr"
 
 
 class suppress:
@@ -227,14 +250,21 @@ class suppress:
 
 
 # Context manipulation is Python 3 only
-if str is not bytes:
+_HAVE_EXCEPTION_CHAINING = sys.version_info.major >= 3
+if _HAVE_EXCEPTION_CHAINING:
     def _make_context_fixer(frame_exc):
         def _fix_exception_context(new_exc, old_exc):
+            # Context may not be correct, so find the end of the chain
             while 1:
                 exc_context = new_exc.__context__
-                if exc_context in (None, frame_exc):
+                if exc_context is old_exc:
+                    # Context is already set correctly (see issue 20317)
+                    return
+                if exc_context is None or exc_context is frame_exc:
                     break
                 new_exc = exc_context
+            # Change the end of the chain to point to the exception
+            # we expect it to reference
             new_exc.__context__ = old_exc
         return _fix_exception_context
 
@@ -258,7 +288,6 @@ else:
         exc_type, exc_value, exc_tb = exc_details
         exec ("raise exc_type, exc_value, exc_tb")
 
-
 # Inspired by discussions on http://bugs.python.org/issue13585
 class ExitStack(object):
     """Context manager for dynamic management of a stack of exit callbacks
@@ -375,6 +404,11 @@ class ExitStack(object):
 class ContextStack(ExitStack):
     """Backwards compatibility alias for ExitStack"""
 
+    def __init__(self):
+        warnings.warn("ContextStack has been renamed to ExitStack",
+                      DeprecationWarning)
+        super(ContextStack, self).__init__()
+
     def register_exit(self, callback):
         return self.push(callback)
 

test_contextlib2.py

@@ -1,50 +1,21 @@
-#!/usr/bin/env python
-"""Unit tests for contextlib2"""
+"""Unit tests for contextlib2.py"""
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import io
 import sys
-
-# Check for a sufficiently recent unittest module
 import unittest
-if not hasattr(unittest, "skipIf"):
-    import unittest2 as unittest
-
-# Handle 2/3 compatibility for redirect_stdout testing,
-# checking 3.x only implicit exception chaining behaviour
-# and checking for exception details in test cases
-if str is bytes:
-    # Python 2
-    from io import BytesIO as StrIO
-    check_exception_chaining = False
-
-    def check_exception_details(case, exc_type, regex):
-        return case.assertRaisesRegexp(exc_type, regex)
-else:
-    # Python 3
-    from io import StringIO as StrIO
-    check_exception_chaining = True
-
-    def check_exception_details(case, exc_type, regex):
-        return case.assertRaisesRegex(exc_type, regex)
-
-
+import __future__ # For PEP 479 conditional test
+import contextlib2
 from contextlib2 import *  # Tests __all__
 
-class ContextManagerTestCase(unittest.TestCase):
+if not hasattr(unittest.TestCase, "assertRaisesRegex"):
+    import unittest2 as unittest
 
-    def test_instance_docstring_given_function_docstring(self):
-        # Issue 19330: ensure context manager instances have good docstrings
-        # See http://bugs.python.org/issue19404 for why this doesn't currently
-        # affect help() output :(
-        def gen_with_docstring():
-            """This has a docstring"""
-            yield
-        gen_docstring = gen_with_docstring.__doc__
-        cm_with_docstring = contextmanager(gen_with_docstring)
-        self.assertEqual(cm_with_docstring.__doc__, gen_docstring)
-        obj = cm_with_docstring()
-        self.assertEqual(obj.__doc__, gen_docstring)
-        self.assertNotEqual(obj.__doc__, type(obj).__doc__)
+requires_docstrings = unittest.skipIf(sys.flags.optimize >= 2,
+                                      "Test requires docstrings")
+
+class ContextManagerTestCase(unittest.TestCase):
 
     def test_contextmanager_plain(self):
         state = []
@@ -115,6 +86,44 @@ class ContextManagerTestCase(unittest.TestCase):
             raise ZeroDivisionError(999)
         self.assertEqual(state, [1, 42, 999])
 
+    def test_contextmanager_except_stopiter(self):
+        stop_exc = StopIteration('spam')
+        @contextmanager
+        def woohoo():
+            yield
+        try:
+            with self.assertWarnsRegex(PendingDeprecationWarning,
+                                       "StopIteration"):
+                with woohoo():
+                    raise stop_exc
+        except Exception as ex:
+            self.assertIs(ex, stop_exc)
+        else:
+            self.fail('StopIteration was suppressed')
+
+    @unittest.skipUnless(hasattr(__future__, "generator_stop"),
+                         "Test only valid for versions implementing PEP 479")
+    def test_contextmanager_except_pep479(self):
+        code = """\
+from __future__ import generator_stop
+from contextlib import contextmanager
+@contextmanager
+def woohoo():
+    yield
+"""
+        locals = {}
+        exec(code, locals, locals)
+        woohoo = locals['woohoo']
+
+        stop_exc = StopIteration('spam')
+        try:
+            with woohoo():
+                raise stop_exc
+        except Exception as ex:
+            self.assertIs(ex, stop_exc)
+        else:
+            self.fail('StopIteration was suppressed')
+
     def _create_contextmanager_attribs(self):
         def attribs(**kw):
             def decorate(func):
@@ -133,14 +142,28 @@ class ContextManagerTestCase(unittest.TestCase):
         self.assertEqual(baz.__name__,'baz')
         self.assertEqual(baz.foo, 'bar')
 
-    @unittest.skipIf(sys.flags.optimize >= 2,
-                     "Docstrings are omitted with -O2 and above")
+    @requires_docstrings
     def test_contextmanager_doc_attrib(self):
         baz = self._create_contextmanager_attribs()
         self.assertEqual(baz.__doc__, "Whee!")
 
+    @requires_docstrings
+    def test_instance_docstring_given_cm_docstring(self):
+        baz = self._create_contextmanager_attribs()(None)
+        self.assertEqual(baz.__doc__, "Whee!")
+
+    def test_keywords(self):
+        # Ensure no keyword arguments are inhibited
+        @contextmanager
+        def woohoo(self, func, args, kwds):
+            yield (self, func, args, kwds)
+        with woohoo(self=11, func=22, args=33, kwds=44) as target:
+            self.assertEqual(target, (11, 22, 33, 44))
+
+
 class ClosingTestCase(unittest.TestCase):
 
+    @requires_docstrings
     def test_instance_docs(self):
         # Issue 19330: ensure context manager instances have good docstrings
         cm_docstring = closing.__doc__
@@ -189,6 +212,7 @@ class mycontext(ContextDecorator):
 
 class TestContextDecorator(unittest.TestCase):
 
+    @requires_docstrings
     def test_instance_docs(self):
         # Issue 19330: ensure context manager instances have good docstrings
         cm_docstring = mycontext.__doc__
@@ -207,7 +231,7 @@ class TestContextDecorator(unittest.TestCase):
     def test_contextdecorator_with_exception(self):
         context = mycontext()
 
-        with check_exception_details(self, NameError, 'foo'):
+        with self.assertRaisesRegex(NameError, 'foo'):
             with context:
                 raise NameError('foo')
         self.assertIsNotNone(context.exc)
@@ -241,7 +265,7 @@ class TestContextDecorator(unittest.TestCase):
             self.assertTrue(context.started)
             raise NameError('foo')
 
-        with check_exception_details(self, NameError, 'foo'):
+        with self.assertRaisesRegex(NameError, 'foo'):
             test()
         self.assertIsNotNone(context.exc)
         self.assertIs(context.exc[0], NameError)
@@ -345,9 +369,12 @@ class TestContextDecorator(unittest.TestCase):
         test('something else')
         self.assertEqual(state, [1, 'something else', 999])
 
+# Detailed exception chaining checks only make sense on Python 3
+check_exception_chaining = contextlib2._HAVE_EXCEPTION_CHAINING
 
 class TestExitStack(unittest.TestCase):
 
+    @requires_docstrings
     def test_instance_docs(self):
         # Issue 19330: ensure context manager instances have good docstrings
         cm_docstring = ExitStack.__doc__
@@ -479,10 +506,7 @@ class TestExitStack(unittest.TestCase):
     def test_exit_exception_chaining_reference(self):
         # Sanity check to make sure that ExitStack chaining matches
         # actual nested with statements
-        # We still run this under Py2, but the only thing it actually
-        # checks in that case is that the outermost exception is IndexError
-        # and that the inner ValueError was suppressed
-        class RaiseExc(object):
+        class RaiseExc:
             def __init__(self, exc):
                 self.exc = exc
             def __enter__(self):
@@ -490,7 +514,7 @@ class TestExitStack(unittest.TestCase):
             def __exit__(self, *exc_details):
                 raise self.exc
 
-        class RaiseExcWithContext(object):
+        class RaiseExcWithContext:
             def __init__(self, outer, inner):
                 self.outer = outer
                 self.inner = inner
@@ -502,11 +526,11 @@ class TestExitStack(unittest.TestCase):
                 except:
                     raise self.outer
 
-        class SuppressExc(object):
+        class SuppressExc:
             def __enter__(self):
                 return self
             def __exit__(self, *exc_details):
-                type(self).saved_details = exc_details
+                self.__class__.saved_details = exc_details
                 return True
 
         try:
@@ -531,15 +555,12 @@ class TestExitStack(unittest.TestCase):
 
     def test_exit_exception_chaining(self):
         # Ensure exception chaining matches the reference behaviour
-        # We still run this under Py2, but the only thing it actually
-        # checks in that case is that the outermost exception is IndexError
-        # and that the inner ValueError was suppressed
         def raise_exc(exc):
             raise exc
 
-        saved_details = []
+        saved_details = [None]
         def suppress_exc(*exc_details):
-            saved_details[:] = [exc_details]
+            saved_details[0] = exc_details
             return True
 
         try:
@@ -591,6 +612,69 @@ class TestExitStack(unittest.TestCase):
         else:
             self.fail("Expected KeyError, but no exception was raised")
 
+    def test_exit_exception_with_correct_context(self):
+        # http://bugs.python.org/issue20317
+        @contextmanager
+        def gets_the_context_right(exc):
+            try:
+                yield
+            finally:
+                raise exc
+
+        exc1 = Exception(1)
+        exc2 = Exception(2)
+        exc3 = Exception(3)
+        exc4 = Exception(4)
+
+        # The contextmanager already fixes the context, so prior to the
+        # fix, ExitStack would try to fix it *again* and get into an
+        # infinite self-referential loop
+        try:
+            with ExitStack() as stack:
+                stack.enter_context(gets_the_context_right(exc4))
+                stack.enter_context(gets_the_context_right(exc3))
+                stack.enter_context(gets_the_context_right(exc2))
+                raise exc1
+        except Exception as exc:
+            self.assertIs(exc, exc4)
+            if check_exception_chaining:
+                self.assertIs(exc.__context__, exc3)
+                self.assertIs(exc.__context__.__context__, exc2)
+                self.assertIs(exc.__context__.__context__.__context__, exc1)
+                self.assertIsNone(
+                        exc.__context__.__context__.__context__.__context__)
+
+    def test_exit_exception_with_existing_context(self):
+        # Addresses a lack of test coverage discovered after checking in a
+        # fix for issue 20317 that still contained debugging code.
+        def raise_nested(inner_exc, outer_exc):
+            try:
+                raise inner_exc
+            finally:
+                raise outer_exc
+        exc1 = Exception(1)
+        exc2 = Exception(2)
+        exc3 = Exception(3)
+        exc4 = Exception(4)
+        exc5 = Exception(5)
+        try:
+            with ExitStack() as stack:
+                stack.callback(raise_nested, exc4, exc5)
+                stack.callback(raise_nested, exc2, exc3)
+                raise exc1
+        except Exception as exc:
+            self.assertIs(exc, exc5)
+            if check_exception_chaining:
+                self.assertIs(exc.__context__, exc4)
+                self.assertIs(exc.__context__.__context__, exc3)
+                self.assertIs(exc.__context__.__context__.__context__, exc2)
+                self.assertIs(
+                    exc.__context__.__context__.__context__.__context__, exc1)
+                self.assertIsNone(
+                    exc.__context__.__context__.__context__.__context__.__context__)
+
+
+
     def test_body_exception_suppress(self):
         def suppress_exc(*exc_details):
             return True
@@ -622,51 +706,79 @@ class TestExitStack(unittest.TestCase):
         stack.push(cm)
         self.assertIs(stack._exit_callbacks[-1], cm)
 
-class TestRedirectStdout(unittest.TestCase):
 
+class TestRedirectStream:
+
+    redirect_stream = None
+    orig_stream = None
+
+    @requires_docstrings
     def test_instance_docs(self):
         # Issue 19330: ensure context manager instances have good docstrings
-        cm_docstring = redirect_stdout.__doc__
-        obj = redirect_stdout(None)
+        cm_docstring = self.redirect_stream.__doc__
+        obj = self.redirect_stream(None)
         self.assertEqual(obj.__doc__, cm_docstring)
 
+    def test_no_redirect_in_init(self):
+        orig_stdout = getattr(sys, self.orig_stream)
+        self.redirect_stream(None)
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+
     def test_redirect_to_string_io(self):
-        f = StrIO()
+        f = io.StringIO()
         msg = "Consider an API like help(), which prints directly to stdout"
-        with redirect_stdout(f):
-            print(msg)
+        orig_stdout = getattr(sys, self.orig_stream)
+        with self.redirect_stream(f):
+            print(msg, file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
         s = f.getvalue().strip()
         self.assertEqual(s, msg)
 
     def test_enter_result_is_target(self):
-        f = StrIO()
-        with redirect_stdout(f) as enter_result:
+        f = io.StringIO()
+        with self.redirect_stream(f) as enter_result:
             self.assertIs(enter_result, f)
 
     def test_cm_is_reusable(self):
-        f = StrIO()
-        write_to_f = redirect_stdout(f)
+        f = io.StringIO()
+        write_to_f = self.redirect_stream(f)
+        orig_stdout = getattr(sys, self.orig_stream)
         with write_to_f:
-            print("Hello")
+            print("Hello", end=" ", file=getattr(sys, self.orig_stream))
         with write_to_f:
-            print("World!")
+            print("World!", file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
         s = f.getvalue()
-        self.assertEqual(s, "Hello\nWorld!\n")
+        self.assertEqual(s, "Hello World!\n")
 
-    # If this is ever made reentrant, update the reusable-but-not-reentrant
-    # example at the end of the contextlib docs accordingly.
-    def test_nested_reentry_fails(self):
-        f = StrIO()
-        write_to_f = redirect_stdout(f)
-        with check_exception_details(self, RuntimeError, "Cannot reenter"):
+    def test_cm_is_reentrant(self):
+        f = io.StringIO()
+        write_to_f = self.redirect_stream(f)
+        orig_stdout = getattr(sys, self.orig_stream)
+        with write_to_f:
+            print("Hello", end=" ", file=getattr(sys, self.orig_stream))
             with write_to_f:
-                print("Hello")
-                with write_to_f:
-                    print("World!")
+                print("World!", file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+        s = f.getvalue()
+        self.assertEqual(s, "Hello World!\n")
+
+
+class TestRedirectStdout(TestRedirectStream, unittest.TestCase):
+
+    redirect_stream = redirect_stdout
+    orig_stream = "stdout"
+
+
+class TestRedirectStderr(TestRedirectStream, unittest.TestCase):
+
+    redirect_stream = redirect_stderr
+    orig_stream = "stderr"
 
 
 class TestSuppress(unittest.TestCase):
 
+    @requires_docstrings
     def test_instance_docs(self):
         # Issue 19330: ensure context manager instances have good docstrings
         cm_docstring = suppress.__doc__
@@ -712,131 +824,12 @@ class TestSuppress(unittest.TestCase):
         with ignore_exceptions:
             len(5)
         with ignore_exceptions:
-            1/0
             with ignore_exceptions: # Check nested usage
                 len(5)
-
-class TestContextStack(unittest.TestCase):
-
-    def test_no_resources(self):
-        with ContextStack():
-            pass
-
-    def test_register(self):
-        expected = [
-            ((), {}),
-            ((1,), {}),
-            ((1,2), {}),
-            ((), dict(example=1)),
-            ((1,), dict(example=1)),
-            ((1,2), dict(example=1)),
-        ]
-        result = []
-        def _exit(*args, **kwds):
-            """Test metadata propagation"""
-            result.append((args, kwds))
-        with ContextStack() as stack:
-            for args, kwds in reversed(expected):
-                if args and kwds:
-                    f = stack.register(_exit, *args, **kwds)
-                elif args:
-                    f = stack.register(_exit, *args)
-                elif kwds:
-                    f = stack.register(_exit, **kwds)
-                else:
-                    f = stack.register(_exit)
-                self.assertIs(f, _exit)
-            for wrapper in stack._exit_callbacks:
-                self.assertIs(wrapper.__wrapped__, _exit)
-                self.assertNotEqual(wrapper.__name__, _exit.__name__)
-                self.assertIsNone(wrapper.__doc__, _exit.__doc__)
-        self.assertEqual(result, expected)
-
-    def test_register_exit(self):
-        exc_raised = ZeroDivisionError
-        def _expect_exc(exc_type, exc, exc_tb):
-            self.assertIs(exc_type, exc_raised)
-        def _suppress_exc(*exc_details):
-            return True
-        def _expect_ok(exc_type, exc, exc_tb):
-            self.assertIsNone(exc_type)
-            self.assertIsNone(exc)
-            self.assertIsNone(exc_tb)
-        class ExitCM(object):
-            def __init__(self, check_exc):
-                self.check_exc = check_exc
-            def __enter__(self):
-                self.fail("Should not be called!")
-            def __exit__(self, *exc_details):
-                self.check_exc(*exc_details)
-        with ContextStack() as stack:
-            stack.register_exit(_expect_ok)
-            self.assertIs(stack._exit_callbacks[-1], _expect_ok)
-            cm = ExitCM(_expect_ok)
-            stack.register_exit(cm)
-            self.assertIs(stack._exit_callbacks[-1].__self__, cm)
-            stack.register_exit(_suppress_exc)
-            self.assertIs(stack._exit_callbacks[-1], _suppress_exc)
-            cm = ExitCM(_expect_exc)
-            stack.register_exit(cm)
-            self.assertIs(stack._exit_callbacks[-1].__self__, cm)
-            stack.register_exit(_expect_exc)
-            self.assertIs(stack._exit_callbacks[-1], _expect_exc)
-            stack.register_exit(_expect_exc)
-            self.assertIs(stack._exit_callbacks[-1], _expect_exc)
+            outer_continued = True
             1/0
-
-    def test_enter_context(self):
-        class TestCM(object):
-            def __enter__(self):
-                result.append(1)
-            def __exit__(self, *exc_details):
-                result.append(3)
-
-        result = []
-        cm = TestCM()
-        with ContextStack() as stack:
-            @stack.register  # Registered first => cleaned up last
-            def _exit():
-                result.append(4)
-            self.assertIsNotNone(_exit)
-            stack.enter_context(cm)
-            self.assertIs(stack._exit_callbacks[-1].__self__, cm)
-            result.append(2)
-        self.assertEqual(result, [1, 2, 3, 4])
-
-    def test_close(self):
-        result = []
-        with ContextStack() as stack:
-            @stack.register
-            def _exit():
-                result.append(1)
-            self.assertIsNotNone(_exit)
-            stack.close()
-            result.append(2)
-        self.assertEqual(result, [1, 2])
-
-    def test_preserve(self):
-        result = []
-        with ContextStack() as stack:
-            @stack.register
-            def _exit():
-                result.append(3)
-            self.assertIsNotNone(_exit)
-            new_stack = stack.preserve()
-            result.append(1)
-        result.append(2)
-        new_stack.close()
-        self.assertEqual(result, [1, 2, 3])
-
-    def test_instance_bypass(self):
-        class Example(object): pass
-        cm = Example()
-        cm.__exit__ = object()
-        stack = ContextStack()
-        self.assertRaises(AttributeError, stack.enter_context, cm)
-        stack.register_exit(cm)
-        self.assertIs(stack._exit_callbacks[-1], cm)
+        self.assertTrue(outer_continued)
 
 if __name__ == "__main__":
+    import unittest
     unittest.main()