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Copy pathtest_contextlib.py
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1366 lines (1156 loc) · 43.3 KB
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"""Unit tests for contextlib.py, and other context managers."""
import io
import os
import sys
import tempfile
import threading
import traceback
import unittest
from contextlib import * # Tests __all__
from test import support
from test.support import os_helper
from test.support.testcase import ExceptionIsLikeMixin
import weakref
class TestAbstractContextManager(unittest.TestCase):
def test_enter(self):
class DefaultEnter(AbstractContextManager):
def __exit__(self, *args):
super().__exit__(*args)
manager = DefaultEnter()
self.assertIs(manager.__enter__(), manager)
def test_slots(self):
class DefaultContextManager(AbstractContextManager):
__slots__ = ()
def __exit__(self, *args):
super().__exit__(*args)
with self.assertRaises(AttributeError):
DefaultContextManager().var = 42
def test_exit_is_abstract(self):
class MissingExit(AbstractContextManager):
pass
with self.assertRaises(TypeError):
MissingExit()
def test_structural_subclassing(self):
class ManagerFromScratch:
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
return None
self.assertIsSubclass(ManagerFromScratch, AbstractContextManager)
class DefaultEnter(AbstractContextManager):
def __exit__(self, *args):
super().__exit__(*args)
self.assertIsSubclass(DefaultEnter, AbstractContextManager)
class NoEnter(ManagerFromScratch):
__enter__ = None
self.assertNotIsSubclass(NoEnter, AbstractContextManager)
class NoExit(ManagerFromScratch):
__exit__ = None
self.assertNotIsSubclass(NoExit, AbstractContextManager)
class ContextManagerTestCase(unittest.TestCase):
def test_contextmanager_plain(self):
state = []
@contextmanager
def woohoo():
state.append(1)
yield 42
state.append(999)
with woohoo() as x:
self.assertEqual(state, [1])
self.assertEqual(x, 42)
state.append(x)
self.assertEqual(state, [1, 42, 999])
def test_contextmanager_finally(self):
state = []
@contextmanager
def woohoo():
state.append(1)
try:
yield 42
finally:
state.append(999)
with self.assertRaises(ZeroDivisionError):
with woohoo() as x:
self.assertEqual(state, [1])
self.assertEqual(x, 42)
state.append(x)
raise ZeroDivisionError()
self.assertEqual(state, [1, 42, 999])
def test_contextmanager_traceback(self):
@contextmanager
def f():
yield
try:
with f():
1/0
except ZeroDivisionError as e:
frames = traceback.extract_tb(e.__traceback__)
self.assertEqual(len(frames), 1)
self.assertEqual(frames[0].name, 'test_contextmanager_traceback')
self.assertEqual(frames[0].line, '1/0')
# Repeat with RuntimeError (which goes through a different code path)
class RuntimeErrorSubclass(RuntimeError):
pass
try:
with f():
raise RuntimeErrorSubclass(42)
except RuntimeErrorSubclass as e:
frames = traceback.extract_tb(e.__traceback__)
self.assertEqual(len(frames), 1)
self.assertEqual(frames[0].name, 'test_contextmanager_traceback')
self.assertEqual(frames[0].line, 'raise RuntimeErrorSubclass(42)')
class StopIterationSubclass(StopIteration):
pass
for stop_exc in (
StopIteration('spam'),
StopIterationSubclass('spam'),
):
with self.subTest(type=type(stop_exc)):
try:
with f():
raise stop_exc
except type(stop_exc) as e:
self.assertIs(e, stop_exc)
frames = traceback.extract_tb(e.__traceback__)
else:
self.fail(f'{stop_exc} was suppressed')
self.assertEqual(len(frames), 1)
self.assertEqual(frames[0].name, 'test_contextmanager_traceback')
self.assertEqual(frames[0].line, 'raise stop_exc')
def test_contextmanager_no_reraise(self):
@contextmanager
def whee():
yield
ctx = whee()
ctx.__enter__()
# Calling __exit__ should not result in an exception
self.assertFalse(ctx.__exit__(TypeError, TypeError("foo"), None))
def test_contextmanager_trap_yield_after_throw(self):
@contextmanager
def whoo():
try:
yield
except:
yield
ctx = whoo()
ctx.__enter__()
with self.assertRaises(RuntimeError):
ctx.__exit__(TypeError, TypeError("foo"), None)
if support.check_impl_detail(cpython=True):
# The "gen" attribute is an implementation detail.
self.assertFalse(ctx.gen.gi_suspended)
def test_contextmanager_trap_no_yield(self):
@contextmanager
def whoo():
if False:
yield
ctx = whoo()
with self.assertRaises(RuntimeError):
ctx.__enter__()
def test_contextmanager_trap_second_yield(self):
@contextmanager
def whoo():
yield
yield
ctx = whoo()
ctx.__enter__()
with self.assertRaises(RuntimeError):
ctx.__exit__(None, None, None)
if support.check_impl_detail(cpython=True):
# The "gen" attribute is an implementation detail.
self.assertFalse(ctx.gen.gi_suspended)
def test_contextmanager_non_normalised(self):
@contextmanager
def whoo():
try:
yield
except RuntimeError:
raise SyntaxError
ctx = whoo()
ctx.__enter__()
with self.assertRaises(SyntaxError):
ctx.__exit__(RuntimeError, None, None)
def test_contextmanager_except(self):
state = []
@contextmanager
def woohoo():
state.append(1)
try:
yield 42
except ZeroDivisionError as e:
state.append(e.args[0])
self.assertEqual(state, [1, 42, 999])
with woohoo() as x:
self.assertEqual(state, [1])
self.assertEqual(x, 42)
state.append(x)
raise ZeroDivisionError(999)
self.assertEqual(state, [1, 42, 999])
def test_contextmanager_except_stopiter(self):
@contextmanager
def woohoo():
yield
class StopIterationSubclass(StopIteration):
pass
for stop_exc in (StopIteration('spam'), StopIterationSubclass('spam')):
with self.subTest(type=type(stop_exc)):
try:
with woohoo():
raise stop_exc
except Exception as ex:
self.assertIs(ex, stop_exc)
else:
self.fail(f'{stop_exc} was suppressed')
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 test_contextmanager_do_not_unchain_non_stopiteration_exceptions(self):
@contextmanager
def test_issue29692():
try:
yield
except Exception as exc:
raise RuntimeError('issue29692:Chained') from exc
try:
with test_issue29692():
raise ZeroDivisionError
except Exception as ex:
self.assertIs(type(ex), RuntimeError)
self.assertEqual(ex.args[0], 'issue29692:Chained')
self.assertIsInstance(ex.__cause__, ZeroDivisionError)
try:
with test_issue29692():
raise StopIteration('issue29692:Unchained')
except Exception as ex:
self.assertIs(type(ex), StopIteration)
self.assertEqual(ex.args[0], 'issue29692:Unchained')
self.assertIsNone(ex.__cause__)
def test_contextmanager_wrap_runtimeerror(self):
@contextmanager
def woohoo():
try:
yield
except Exception as exc:
raise RuntimeError(f'caught {exc}') from exc
with self.assertRaises(RuntimeError):
with woohoo():
1 / 0
# If the context manager wrapped StopIteration in a RuntimeError,
# we also unwrap it, because we can't tell whether the wrapping was
# done by the generator machinery or by the generator itself.
with self.assertRaises(StopIteration):
with woohoo():
raise StopIteration
def _create_contextmanager_attribs(self):
def attribs(**kw):
def decorate(func):
for k,v in kw.items():
setattr(func,k,v)
return func
return decorate
@contextmanager
@attribs(foo='bar')
def baz(spam):
"""Whee!"""
yield
return baz
def test_contextmanager_attribs(self):
baz = self._create_contextmanager_attribs()
self.assertEqual(baz.__name__,'baz')
self.assertEqual(baz.foo, 'bar')
@support.requires_docstrings
def test_contextmanager_doc_attrib(self):
baz = self._create_contextmanager_attribs()
self.assertEqual(baz.__doc__, "Whee!")
@support.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))
def test_nokeepref(self):
class A:
pass
@contextmanager
def woohoo(a, b):
a = weakref.ref(a)
b = weakref.ref(b)
# Allow test to work with a non-refcounted GC
support.gc_collect()
self.assertIsNone(a())
self.assertIsNone(b())
yield
with woohoo(A(), b=A()):
pass
def test_param_errors(self):
@contextmanager
def woohoo(a, *, b):
yield
with self.assertRaises(TypeError):
woohoo()
with self.assertRaises(TypeError):
woohoo(3, 5)
with self.assertRaises(TypeError):
woohoo(b=3)
def test_recursive(self):
depth = 0
ncols = 0
@contextmanager
def woohoo():
nonlocal ncols
ncols += 1
nonlocal depth
before = depth
depth += 1
yield
depth -= 1
self.assertEqual(depth, before)
@woohoo()
def recursive():
if depth < 10:
recursive()
recursive()
self.assertEqual(ncols, 10)
self.assertEqual(depth, 0)
class ClosingTestCase(unittest.TestCase):
@support.requires_docstrings
def test_instance_docs(self):
# Issue 19330: ensure context manager instances have good docstrings
cm_docstring = closing.__doc__
obj = closing(None)
self.assertEqual(obj.__doc__, cm_docstring)
def test_closing(self):
state = []
class C:
def close(self):
state.append(1)
x = C()
self.assertEqual(state, [])
with closing(x) as y:
self.assertEqual(x, y)
self.assertEqual(state, [1])
def test_closing_error(self):
state = []
class C:
def close(self):
state.append(1)
x = C()
self.assertEqual(state, [])
with self.assertRaises(ZeroDivisionError):
with closing(x) as y:
self.assertEqual(x, y)
1 / 0
self.assertEqual(state, [1])
class NullcontextTestCase(unittest.TestCase):
def test_nullcontext(self):
class C:
pass
c = C()
with nullcontext(c) as c_in:
self.assertIs(c_in, c)
class FileContextTestCase(unittest.TestCase):
def testWithOpen(self):
tfn = tempfile.mktemp()
try:
with open(tfn, "w", encoding="utf-8") as f:
self.assertFalse(f.closed)
f.write("Booh\n")
self.assertTrue(f.closed)
with self.assertRaises(ZeroDivisionError):
with open(tfn, "r", encoding="utf-8") as f:
self.assertFalse(f.closed)
self.assertEqual(f.read(), "Booh\n")
1 / 0
self.assertTrue(f.closed)
finally:
os_helper.unlink(tfn)
class LockContextTestCase(unittest.TestCase):
def boilerPlate(self, lock, locked):
self.assertFalse(locked())
with lock:
self.assertTrue(locked())
self.assertFalse(locked())
with self.assertRaises(ZeroDivisionError):
with lock:
self.assertTrue(locked())
1 / 0
self.assertFalse(locked())
def testWithLock(self):
lock = threading.Lock()
self.boilerPlate(lock, lock.locked)
def testWithRLock(self):
lock = threading.RLock()
self.boilerPlate(lock, lock._is_owned)
def testWithCondition(self):
lock = threading.Condition()
def locked():
return lock._is_owned()
self.boilerPlate(lock, locked)
def testWithSemaphore(self):
lock = threading.Semaphore()
def locked():
if lock.acquire(False):
lock.release()
return False
else:
return True
self.boilerPlate(lock, locked)
def testWithBoundedSemaphore(self):
lock = threading.BoundedSemaphore()
def locked():
if lock.acquire(False):
lock.release()
return False
else:
return True
self.boilerPlate(lock, locked)
class mycontext(ContextDecorator):
"""Example decoration-compatible context manager for testing"""
started = False
exc = None
catch = False
def __enter__(self):
self.started = True
return self
def __exit__(self, *exc):
self.exc = exc
return self.catch
class TestContextDecorator(unittest.TestCase):
@support.requires_docstrings
def test_instance_docs(self):
# Issue 19330: ensure context manager instances have good docstrings
cm_docstring = mycontext.__doc__
obj = mycontext()
self.assertEqual(obj.__doc__, cm_docstring)
def test_contextdecorator(self):
context = mycontext()
with context as result:
self.assertIs(result, context)
self.assertTrue(context.started)
self.assertEqual(context.exc, (None, None, None))
def test_contextdecorator_with_exception(self):
context = mycontext()
with self.assertRaisesRegex(NameError, 'foo'):
with context:
raise NameError('foo')
self.assertIsNotNone(context.exc)
self.assertIs(context.exc[0], NameError)
context = mycontext()
context.catch = True
with context:
raise NameError('foo')
self.assertIsNotNone(context.exc)
self.assertIs(context.exc[0], NameError)
def test_decorator(self):
context = mycontext()
@context
def test():
self.assertIsNone(context.exc)
self.assertTrue(context.started)
test()
self.assertEqual(context.exc, (None, None, None))
def test_decorator_with_exception(self):
context = mycontext()
@context
def test():
self.assertIsNone(context.exc)
self.assertTrue(context.started)
raise NameError('foo')
with self.assertRaisesRegex(NameError, 'foo'):
test()
self.assertIsNotNone(context.exc)
self.assertIs(context.exc[0], NameError)
def test_decorating_method(self):
context = mycontext()
class Test(object):
@context
def method(self, a, b, c=None):
self.a = a
self.b = b
self.c = c
# these tests are for argument passing when used as a decorator
test = Test()
test.method(1, 2)
self.assertEqual(test.a, 1)
self.assertEqual(test.b, 2)
self.assertEqual(test.c, None)
test = Test()
test.method('a', 'b', 'c')
self.assertEqual(test.a, 'a')
self.assertEqual(test.b, 'b')
self.assertEqual(test.c, 'c')
test = Test()
test.method(a=1, b=2)
self.assertEqual(test.a, 1)
self.assertEqual(test.b, 2)
def test_typo_enter(self):
class mycontext(ContextDecorator):
def __unter__(self):
pass
def __exit__(self, *exc):
pass
with self.assertRaisesRegex(TypeError, 'the context manager'):
with mycontext():
pass
def test_typo_exit(self):
class mycontext(ContextDecorator):
def __enter__(self):
pass
def __uxit__(self, *exc):
pass
with self.assertRaisesRegex(TypeError, 'the context manager.*__exit__'):
with mycontext():
pass
def test_contextdecorator_as_mixin(self):
class somecontext(object):
started = False
exc = None
def __enter__(self):
self.started = True
return self
def __exit__(self, *exc):
self.exc = exc
class mycontext(somecontext, ContextDecorator):
pass
context = mycontext()
@context
def test():
self.assertIsNone(context.exc)
self.assertTrue(context.started)
test()
self.assertEqual(context.exc, (None, None, None))
def test_contextmanager_as_decorator(self):
@contextmanager
def woohoo(y):
state.append(y)
yield
state.append(999)
state = []
@woohoo(1)
def test(x):
self.assertEqual(state, [1])
state.append(x)
test('something')
self.assertEqual(state, [1, 'something', 999])
# Issue #11647: Ensure the decorated function is 'reusable'
state = []
test('something else')
self.assertEqual(state, [1, 'something else', 999])
class TestBaseExitStack:
exit_stack = None
@support.requires_docstrings
def test_instance_docs(self):
# Issue 19330: ensure context manager instances have good docstrings
cm_docstring = self.exit_stack.__doc__
obj = self.exit_stack()
self.assertEqual(obj.__doc__, cm_docstring)
def test_no_resources(self):
with self.exit_stack():
pass
def test_callback(self):
expected = [
((), {}),
((1,), {}),
((1,2), {}),
((), dict(example=1)),
((1,), dict(example=1)),
((1,2), dict(example=1)),
((1,2), dict(self=3, callback=4)),
]
result = []
def _exit(*args, **kwds):
"""Test metadata propagation"""
result.append((args, kwds))
with self.exit_stack() as stack:
for args, kwds in reversed(expected):
if args and kwds:
f = stack.callback(_exit, *args, **kwds)
elif args:
f = stack.callback(_exit, *args)
elif kwds:
f = stack.callback(_exit, **kwds)
else:
f = stack.callback(_exit)
self.assertIs(f, _exit)
for wrapper in stack._exit_callbacks:
self.assertIs(wrapper[1].__wrapped__, _exit)
self.assertNotEqual(wrapper[1].__name__, _exit.__name__)
self.assertIsNone(wrapper[1].__doc__, _exit.__doc__)
self.assertEqual(result, expected)
result = []
with self.exit_stack() as stack:
with self.assertRaises(TypeError):
stack.callback(arg=1)
with self.assertRaises(TypeError):
self.exit_stack.callback(arg=2)
with self.assertRaises(TypeError):
stack.callback(callback=_exit, arg=3)
self.assertEqual(result, [])
def test_push(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 self.exit_stack() as stack:
stack.push(_expect_ok)
self.assertIs(stack._exit_callbacks[-1][1], _expect_ok)
cm = ExitCM(_expect_ok)
stack.push(cm)
self.assertIs(stack._exit_callbacks[-1][1].__self__, cm)
stack.push(_suppress_exc)
self.assertIs(stack._exit_callbacks[-1][1], _suppress_exc)
cm = ExitCM(_expect_exc)
stack.push(cm)
self.assertIs(stack._exit_callbacks[-1][1].__self__, cm)
stack.push(_expect_exc)
self.assertIs(stack._exit_callbacks[-1][1], _expect_exc)
stack.push(_expect_exc)
self.assertIs(stack._exit_callbacks[-1][1], _expect_exc)
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 self.exit_stack() as stack:
@stack.callback # Registered first => cleaned up last
def _exit():
result.append(4)
self.assertIsNotNone(_exit)
stack.enter_context(cm)
self.assertIs(stack._exit_callbacks[-1][1].__self__, cm)
result.append(2)
self.assertEqual(result, [1, 2, 3, 4])
def test_enter_context_errors(self):
class LacksEnterAndExit:
pass
class LacksEnter:
def __exit__(self, *exc_info):
pass
class LacksExit:
def __enter__(self):
pass
with self.exit_stack() as stack:
with self.assertRaisesRegex(TypeError, 'the context manager'):
stack.enter_context(LacksEnterAndExit())
with self.assertRaisesRegex(TypeError, 'the context manager'):
stack.enter_context(LacksEnter())
with self.assertRaisesRegex(TypeError, 'the context manager'):
stack.enter_context(LacksExit())
self.assertFalse(stack._exit_callbacks)
def test_close(self):
result = []
with self.exit_stack() as stack:
@stack.callback
def _exit():
result.append(1)
self.assertIsNotNone(_exit)
stack.close()
result.append(2)
self.assertEqual(result, [1, 2])
def test_pop_all(self):
result = []
with self.exit_stack() as stack:
@stack.callback
def _exit():
result.append(3)
self.assertIsNotNone(_exit)
new_stack = stack.pop_all()
result.append(1)
result.append(2)
new_stack.close()
self.assertEqual(result, [1, 2, 3])
def test_exit_raise(self):
with self.assertRaises(ZeroDivisionError):
with self.exit_stack() as stack:
stack.push(lambda *exc: False)
1/0
def test_exit_suppress(self):
with self.exit_stack() as stack:
stack.push(lambda *exc: True)
1/0
def test_exit_exception_traceback(self):
# This test captures the current behavior of ExitStack so that we know
# if we ever unintendedly change it. It is not a statement of what the
# desired behavior is (for instance, we may want to remove some of the
# internal contextlib frames).
def raise_exc(exc):
raise exc
try:
with self.exit_stack() as stack:
stack.callback(raise_exc, ValueError)
1/0
except ValueError as e:
exc = e
self.assertIsInstance(exc, ValueError)
ve_frames = traceback.extract_tb(exc.__traceback__)
expected = \
[('test_exit_exception_traceback', 'with self.exit_stack() as stack:')] + \
self.callback_error_internal_frames + \
[('_exit_wrapper', 'callback(*args, **kwds)'),
('raise_exc', 'raise exc')]
self.assertEqual(
[(f.name, f.line) for f in ve_frames], expected)
self.assertIsInstance(exc.__context__, ZeroDivisionError)
zde_frames = traceback.extract_tb(exc.__context__.__traceback__)
self.assertEqual([(f.name, f.line) for f in zde_frames],
[('test_exit_exception_traceback', '1/0')])
def test_exit_exception_chaining_reference(self):
# Sanity check to make sure that ExitStack chaining matches
# actual nested with statements
class RaiseExc:
def __init__(self, exc):
self.exc = exc
def __enter__(self):
return self
def __exit__(self, *exc_details):
raise self.exc
class RaiseExcWithContext:
def __init__(self, outer, inner):
self.outer = outer
self.inner = inner
def __enter__(self):
return self
def __exit__(self, *exc_details):
try:
raise self.inner
except:
raise self.outer
class SuppressExc:
def __enter__(self):
return self
def __exit__(self, *exc_details):
type(self).saved_details = exc_details
return True
try:
with RaiseExc(IndexError):
with RaiseExcWithContext(KeyError, AttributeError):
with SuppressExc():
with RaiseExc(ValueError):
1 / 0
except IndexError as exc:
self.assertIsInstance(exc.__context__, KeyError)
self.assertIsInstance(exc.__context__.__context__, AttributeError)
# Inner exceptions were suppressed
self.assertIsNone(exc.__context__.__context__.__context__)
else:
self.fail("Expected IndexError, but no exception was raised")
# Check the inner exceptions
inner_exc = SuppressExc.saved_details[1]
self.assertIsInstance(inner_exc, ValueError)
self.assertIsInstance(inner_exc.__context__, ZeroDivisionError)
def test_exit_exception_chaining(self):
# Ensure exception chaining matches the reference behaviour
def raise_exc(exc):
raise exc
saved_details = None
def suppress_exc(*exc_details):
nonlocal saved_details
saved_details = exc_details
return True
try:
with self.exit_stack() as stack:
stack.callback(raise_exc, IndexError)
stack.callback(raise_exc, KeyError)
stack.callback(raise_exc, AttributeError)
stack.push(suppress_exc)
stack.callback(raise_exc, ValueError)
1 / 0
except IndexError as exc:
self.assertIsInstance(exc.__context__, KeyError)
self.assertIsInstance(exc.__context__.__context__, AttributeError)
# Inner exceptions were suppressed
self.assertIsNone(exc.__context__.__context__.__context__)
else:
self.fail("Expected IndexError, but no exception was raised")
# Check the inner exceptions
inner_exc = saved_details[1]
self.assertIsInstance(inner_exc, ValueError)
self.assertIsInstance(inner_exc.__context__, ZeroDivisionError)
def test_exit_exception_explicit_none_context(self):
# Ensure ExitStack chaining matches actual nested `with` statements
# regarding explicit __context__ = None.
class MyException(Exception):
pass
@contextmanager
def my_cm():
try:
yield
except BaseException:
exc = MyException()
try:
raise exc
finally:
exc.__context__ = None
@contextmanager
def my_cm_with_exit_stack():
with self.exit_stack() as stack:
stack.enter_context(my_cm())
yield stack
for cm in (my_cm, my_cm_with_exit_stack):
with self.subTest():
try:
with cm():
raise IndexError()
except MyException as exc:
self.assertIsNone(exc.__context__)
else:
self.fail("Expected IndexError, but no exception was raised")
def test_exit_exception_non_suppressing(self):
# http://bugs.python.org/issue19092
def raise_exc(exc):
raise exc
def suppress_exc(*exc_details):
return True
try:
with self.exit_stack() as stack:
stack.callback(lambda: None)