diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index b831d8916ca..5b646fabca0 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -20,6 +20,8 @@ class AbstractContextManager(abc.ABC):
 
     __class_getitem__ = classmethod(GenericAlias)
 
+    __slots__ = ()
+
     def __enter__(self):
         """Return `self` upon entering the runtime context."""
         return self
@@ -42,6 +44,8 @@ class AbstractAsyncContextManager(abc.ABC):
 
     __class_getitem__ = classmethod(GenericAlias)
 
+    __slots__ = ()
+
     async def __aenter__(self):
         """Return `self` upon entering the runtime context."""
         return self
@@ -565,11 +569,12 @@ def __enter__(self):
         return self
 
     def __exit__(self, *exc_details):
-        received_exc = exc_details[0] is not None
+        exc = exc_details[1]
+        received_exc = exc is not None
 
         # We manipulate the exception state so it behaves as though
         # we were actually nesting multiple with statements
-        frame_exc = sys.exc_info()[1]
+        frame_exc = sys.exception()
         def _fix_exception_context(new_exc, old_exc):
             # Context may not be correct, so find the end of the chain
             while 1:
@@ -592,24 +597,28 @@ def _fix_exception_context(new_exc, old_exc):
             is_sync, cb = self._exit_callbacks.pop()
             assert is_sync
             try:
+                if exc is None:
+                    exc_details = None, None, None
+                else:
+                    exc_details = type(exc), exc, exc.__traceback__
                 if cb(*exc_details):
                     suppressed_exc = True
                     pending_raise = False
-                    exc_details = (None, None, None)
-            except:
-                new_exc_details = sys.exc_info()
+                    exc = None
+            except BaseException as new_exc:
                 # simulate the stack of exceptions by setting the context
-                _fix_exception_context(new_exc_details[1], exc_details[1])
+                _fix_exception_context(new_exc, exc)
                 pending_raise = True
-                exc_details = new_exc_details
+                exc = new_exc
+
         if pending_raise:
             try:
-                # bare "raise exc_details[1]" replaces our carefully
+                # bare "raise exc" replaces our carefully
                 # set-up context
-                fixed_ctx = exc_details[1].__context__
-                raise exc_details[1]
+                fixed_ctx = exc.__context__
+                raise exc
             except BaseException:
-                exc_details[1].__context__ = fixed_ctx
+                exc.__context__ = fixed_ctx
                 raise
         return received_exc and suppressed_exc
 
@@ -705,11 +714,12 @@ async def __aenter__(self):
         return self
 
     async def __aexit__(self, *exc_details):
-        received_exc = exc_details[0] is not None
+        exc = exc_details[1]
+        received_exc = exc is not None
 
         # We manipulate the exception state so it behaves as though
         # we were actually nesting multiple with statements
-        frame_exc = sys.exc_info()[1]
+        frame_exc = sys.exception()
         def _fix_exception_context(new_exc, old_exc):
             # Context may not be correct, so find the end of the chain
             while 1:
@@ -731,6 +741,10 @@ def _fix_exception_context(new_exc, old_exc):
         while self._exit_callbacks:
             is_sync, cb = self._exit_callbacks.pop()
             try:
+                if exc is None:
+                    exc_details = None, None, None
+                else:
+                    exc_details = type(exc), exc, exc.__traceback__
                 if is_sync:
                     cb_suppress = cb(*exc_details)
                 else:
@@ -739,21 +753,21 @@ def _fix_exception_context(new_exc, old_exc):
                 if cb_suppress:
                     suppressed_exc = True
                     pending_raise = False
-                    exc_details = (None, None, None)
-            except:
-                new_exc_details = sys.exc_info()
+                    exc = None
+            except BaseException as new_exc:
                 # simulate the stack of exceptions by setting the context
-                _fix_exception_context(new_exc_details[1], exc_details[1])
+                _fix_exception_context(new_exc, exc)
                 pending_raise = True
-                exc_details = new_exc_details
+                exc = new_exc
+
         if pending_raise:
             try:
-                # bare "raise exc_details[1]" replaces our carefully
+                # bare "raise exc" replaces our carefully
                 # set-up context
-                fixed_ctx = exc_details[1].__context__
-                raise exc_details[1]
+                fixed_ctx = exc.__context__
+                raise exc
             except BaseException:
-                exc_details[1].__context__ = fixed_ctx
+                exc.__context__ = fixed_ctx
                 raise
         return received_exc and suppressed_exc
 
diff --git a/Lib/test/archivetestdata/README.md b/Lib/test/archivetestdata/README.md
new file mode 100644
index 00000000000..7b555fa3276
--- /dev/null
+++ b/Lib/test/archivetestdata/README.md
@@ -0,0 +1,36 @@
+# Test data for `test_zipfile`, `test_tarfile` (and even some others)
+
+## `test_zipfile`
+
+The test executables in this directory are created manually from `header.sh` and
+the `testdata_module_inside_zip.py` file.  You must have Info-ZIP's zip utility
+installed (`apt install zip` on Debian).
+
+### Purpose of `exe_with_zip` and `exe_with_z64`
+
+These are used to test executable files with an appended zipfile, in a scenario
+where the executable is _not_ a Python interpreter itself so our automatic
+zipimport machinery (that'd look for `__main__.py`) is not being used.
+
+### Updating the test executables
+
+If you update header.sh or the testdata_module_inside_zip.py file, rerun the
+commands below.  These are expected to be rarely changed, if ever.
+
+#### Standard old format (2.0) zip file
+
+```
+zip -0 zip2.zip testdata_module_inside_zip.py
+cat header.sh zip2.zip >exe_with_zip
+rm zip2.zip
+```
+
+#### Modern format (4.5) zip64 file
+
+Redirecting from stdin forces Info-ZIP's zip tool to create a zip64.
+
+```
+zip -0 <testdata_module_inside_zip.py >zip64.zip
+cat header.sh zip64.zip >exe_with_z64
+rm zip64.zip
+```
diff --git a/Lib/test/archivetestdata/exe_with_z64 b/Lib/test/archivetestdata/exe_with_z64
new file mode 100755
index 00000000000..82b03cf39d9
Binary files /dev/null and b/Lib/test/archivetestdata/exe_with_z64 differ
diff --git a/Lib/test/archivetestdata/exe_with_zip b/Lib/test/archivetestdata/exe_with_zip
new file mode 100755
index 00000000000..c833cdf9f93
Binary files /dev/null and b/Lib/test/archivetestdata/exe_with_zip differ
diff --git a/Lib/test/archivetestdata/header.sh b/Lib/test/archivetestdata/header.sh
new file mode 100755
index 00000000000..52dc91acf74
--- /dev/null
+++ b/Lib/test/archivetestdata/header.sh
@@ -0,0 +1,24 @@
+#!/bin/bash
+INTERPRETER_UNDER_TEST="$1"
+if [[ ! -x "${INTERPRETER_UNDER_TEST}" ]]; then
+    echo "Interpreter must be the command line argument."
+    exit 4
+fi
+EXECUTABLE="$0" exec "${INTERPRETER_UNDER_TEST}" -E - <<END_OF_PYTHON
+import os
+import zipfile
+
+namespace = {}
+
+filename = os.environ['EXECUTABLE']
+print(f'Opening {filename} as a zipfile.')
+with zipfile.ZipFile(filename, mode='r') as exe_zip:
+  for file_info in exe_zip.infolist():
+    data = exe_zip.read(file_info)
+    exec(data, namespace, namespace)
+    break  # Only use the first file in the archive.
+
+print('Favorite number in executable:', namespace["FAVORITE_NUMBER"])
+
+### Archive contents will be appended after this file. ###
+END_OF_PYTHON
diff --git a/Lib/test/archivetestdata/recursion.tar b/Lib/test/archivetestdata/recursion.tar
new file mode 100644
index 00000000000..b8237251964
Binary files /dev/null and b/Lib/test/archivetestdata/recursion.tar differ
diff --git a/Lib/test/archivetestdata/testdata_module_inside_zip.py b/Lib/test/archivetestdata/testdata_module_inside_zip.py
new file mode 100644
index 00000000000..6f8dcd6c0e8
--- /dev/null
+++ b/Lib/test/archivetestdata/testdata_module_inside_zip.py
@@ -0,0 +1,2 @@
+# Test data file to be stored within a zip file.
+FAVORITE_NUMBER = 5
diff --git a/Lib/test/archivetestdata/testtar.tar b/Lib/test/archivetestdata/testtar.tar
new file mode 100644
index 00000000000..bb9345373e9
Binary files /dev/null and b/Lib/test/archivetestdata/testtar.tar differ
diff --git a/Lib/test/archivetestdata/testtar.tar.xz b/Lib/test/archivetestdata/testtar.tar.xz
new file mode 100644
index 00000000000..512fa149e6c
Binary files /dev/null and b/Lib/test/archivetestdata/testtar.tar.xz differ
diff --git a/Lib/test/archivetestdata/zip_cp437_header.zip b/Lib/test/archivetestdata/zip_cp437_header.zip
new file mode 100644
index 00000000000..f7c6cf17042
Binary files /dev/null and b/Lib/test/archivetestdata/zip_cp437_header.zip differ
diff --git a/Lib/test/archivetestdata/zipdir.zip b/Lib/test/archivetestdata/zipdir.zip
new file mode 100644
index 00000000000..ac21d7a1edd
Binary files /dev/null and b/Lib/test/archivetestdata/zipdir.zip differ
diff --git a/Lib/test/archivetestdata/zipdir_backslash.zip b/Lib/test/archivetestdata/zipdir_backslash.zip
new file mode 100644
index 00000000000..979126ef5e3
Binary files /dev/null and b/Lib/test/archivetestdata/zipdir_backslash.zip differ
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 91764696ba2..0bde2ecff3f 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -24,6 +24,18 @@ def __exit__(self, *args):
         manager = DefaultEnter()
         self.assertIs(manager.__enter__(), manager)
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    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
@@ -194,6 +206,7 @@ def whoo():
                 yield
             except RuntimeError:
                 raise SyntaxError
+
         ctx = whoo()
         ctx.__enter__()
         with self.assertRaises(SyntaxError):
@@ -285,9 +298,11 @@ def woohoo():
                 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.
@@ -1143,7 +1158,7 @@ def first():
 class TestExitStack(TestBaseExitStack, unittest.TestCase):
     exit_stack = ExitStack
     callback_error_internal_frames = [
-        ('__exit__', 'raise exc_details[1]'),
+        ('__exit__', 'raise exc'),
         ('__exit__', 'if cb(*exc_details):'),
     ]
 
@@ -1294,7 +1309,6 @@ def test_exception_groups(self):
                 [KeyError("ke1"), KeyError("ke2")],
             ),
         )
-
         # Check handling of BaseExceptionGroup, using GeneratorExit so that
         # we don't accidentally discard a ctrl-c with KeyboardInterrupt.
         with suppress(GeneratorExit):
@@ -1338,7 +1352,7 @@ def test_simple(self):
     def test_reentrant(self):
         old_cwd = os.getcwd()
         target1 = self.make_relative_path('data')
-        target2 = self.make_relative_path('ziptestdata')
+        target2 = self.make_relative_path('archivetestdata')
         self.assertNotIn(old_cwd, (target1, target2))
         chdir1, chdir2 = chdir(target1), chdir(target2)
 
diff --git a/Lib/test/test_contextlib_async.py b/Lib/test/test_contextlib_async.py
new file mode 100644
index 00000000000..5673c1b4bc5
--- /dev/null
+++ b/Lib/test/test_contextlib_async.py
@@ -0,0 +1,780 @@
+import asyncio
+from contextlib import (
+    asynccontextmanager, AbstractAsyncContextManager,
+    AsyncExitStack, nullcontext, aclosing, contextmanager)
+from test import support
+import unittest
+import traceback
+
+from test.test_contextlib import TestBaseExitStack
+
+support.requires_working_socket(module=True)
+
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
+class TestAbstractAsyncContextManager(unittest.IsolatedAsyncioTestCase):
+
+    async def test_enter(self):
+        class DefaultEnter(AbstractAsyncContextManager):
+            async def __aexit__(self, *args):
+                await super().__aexit__(*args)
+
+        manager = DefaultEnter()
+        self.assertIs(await manager.__aenter__(), manager)
+
+        async with manager as context:
+            self.assertIs(manager, context)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_slots(self):
+        class DefaultAsyncContextManager(AbstractAsyncContextManager):
+            __slots__ = ()
+
+            async def __aexit__(self, *args):
+                await super().__aexit__(*args)
+
+        with self.assertRaises(AttributeError):
+            manager = DefaultAsyncContextManager()
+            manager.var = 42
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_async_gen_propagates_generator_exit(self):
+        # A regression test for https://bugs.python.org/issue33786.
+
+        @asynccontextmanager
+        async def ctx():
+            yield
+
+        async def gen():
+            async with ctx():
+                yield 11
+
+        g = gen()
+        async for val in g:
+            self.assertEqual(val, 11)
+            break
+        await g.aclose()
+
+    def test_exit_is_abstract(self):
+        class MissingAexit(AbstractAsyncContextManager):
+            pass
+
+        with self.assertRaises(TypeError):
+            MissingAexit()
+
+    def test_structural_subclassing(self):
+        class ManagerFromScratch:
+            async def __aenter__(self):
+                return self
+            async def __aexit__(self, exc_type, exc_value, traceback):
+                return None
+
+        self.assertTrue(issubclass(ManagerFromScratch, AbstractAsyncContextManager))
+
+        class DefaultEnter(AbstractAsyncContextManager):
+            async def __aexit__(self, *args):
+                await super().__aexit__(*args)
+
+        self.assertTrue(issubclass(DefaultEnter, AbstractAsyncContextManager))
+
+        class NoneAenter(ManagerFromScratch):
+            __aenter__ = None
+
+        self.assertFalse(issubclass(NoneAenter, AbstractAsyncContextManager))
+
+        class NoneAexit(ManagerFromScratch):
+            __aexit__ = None
+
+        self.assertFalse(issubclass(NoneAexit, AbstractAsyncContextManager))
+
+
+class AsyncContextManagerTestCase(unittest.IsolatedAsyncioTestCase):
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_plain(self):
+        state = []
+        @asynccontextmanager
+        async def woohoo():
+            state.append(1)
+            yield 42
+            state.append(999)
+        async with woohoo() as x:
+            self.assertEqual(state, [1])
+            self.assertEqual(x, 42)
+            state.append(x)
+        self.assertEqual(state, [1, 42, 999])
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_finally(self):
+        state = []
+        @asynccontextmanager
+        async def woohoo():
+            state.append(1)
+            try:
+                yield 42
+            finally:
+                state.append(999)
+        with self.assertRaises(ZeroDivisionError):
+            async with woohoo() as x:
+                self.assertEqual(state, [1])
+                self.assertEqual(x, 42)
+                state.append(x)
+                raise ZeroDivisionError()
+        self.assertEqual(state, [1, 42, 999])
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_traceback(self):
+        @asynccontextmanager
+        async def f():
+            yield
+
+        try:
+            async 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:
+            async 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
+
+        class StopAsyncIterationSubclass(StopAsyncIteration):
+            pass
+
+        for stop_exc in (
+            StopIteration('spam'),
+            StopAsyncIteration('ham'),
+            StopIterationSubclass('spam'),
+            StopAsyncIterationSubclass('spam')
+        ):
+            with self.subTest(type=type(stop_exc)):
+                try:
+                    async 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')
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_no_reraise(self):
+        @asynccontextmanager
+        async def whee():
+            yield
+        ctx = whee()
+        await ctx.__aenter__()
+        # Calling __aexit__ should not result in an exception
+        self.assertFalse(await ctx.__aexit__(TypeError, TypeError("foo"), None))
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_trap_yield_after_throw(self):
+        @asynccontextmanager
+        async def whoo():
+            try:
+                yield
+            except:
+                yield
+        ctx = whoo()
+        await ctx.__aenter__()
+        with self.assertRaises(RuntimeError):
+            await ctx.__aexit__(TypeError, TypeError('foo'), None)
+        if support.check_impl_detail(cpython=True):
+            # The "gen" attribute is an implementation detail.
+            self.assertFalse(ctx.gen.ag_suspended)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_trap_no_yield(self):
+        @asynccontextmanager
+        async def whoo():
+            if False:
+                yield
+        ctx = whoo()
+        with self.assertRaises(RuntimeError):
+            await ctx.__aenter__()
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_trap_second_yield(self):
+        @asynccontextmanager
+        async def whoo():
+            yield
+            yield
+        ctx = whoo()
+        await ctx.__aenter__()
+        with self.assertRaises(RuntimeError):
+            await ctx.__aexit__(None, None, None)
+        if support.check_impl_detail(cpython=True):
+            # The "gen" attribute is an implementation detail.
+            self.assertFalse(ctx.gen.ag_suspended)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_non_normalised(self):
+        @asynccontextmanager
+        async def whoo():
+            try:
+                yield
+            except RuntimeError:
+                raise SyntaxError
+
+        ctx = whoo()
+        await ctx.__aenter__()
+        with self.assertRaises(SyntaxError):
+            await ctx.__aexit__(RuntimeError, None, None)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_except(self):
+        state = []
+        @asynccontextmanager
+        async def woohoo():
+            state.append(1)
+            try:
+                yield 42
+            except ZeroDivisionError as e:
+                state.append(e.args[0])
+                self.assertEqual(state, [1, 42, 999])
+        async with woohoo() as x:
+            self.assertEqual(state, [1])
+            self.assertEqual(x, 42)
+            state.append(x)
+            raise ZeroDivisionError(999)
+        self.assertEqual(state, [1, 42, 999])
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_except_stopiter(self):
+        @asynccontextmanager
+        async def woohoo():
+            yield
+
+        class StopIterationSubclass(StopIteration):
+            pass
+
+        class StopAsyncIterationSubclass(StopAsyncIteration):
+            pass
+
+        for stop_exc in (
+            StopIteration('spam'),
+            StopAsyncIteration('ham'),
+            StopIterationSubclass('spam'),
+            StopAsyncIterationSubclass('spam')
+        ):
+            with self.subTest(type=type(stop_exc)):
+                try:
+                    async with woohoo():
+                        raise stop_exc
+                except Exception as ex:
+                    self.assertIs(ex, stop_exc)
+                else:
+                    self.fail(f'{stop_exc} was suppressed')
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_contextmanager_wrap_runtimeerror(self):
+        @asynccontextmanager
+        async def woohoo():
+            try:
+                yield
+            except Exception as exc:
+                raise RuntimeError(f'caught {exc}') from exc
+
+        with self.assertRaises(RuntimeError):
+            async with woohoo():
+                1 / 0
+
+        # If the context manager wrapped StopAsyncIteration 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(StopAsyncIteration):
+            async with woohoo():
+                raise StopAsyncIteration
+
+    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
+        @asynccontextmanager
+        @attribs(foo='bar')
+        async 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!")
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    @support.requires_docstrings
+    async def test_instance_docstring_given_cm_docstring(self):
+        baz = self._create_contextmanager_attribs()(None)
+        self.assertEqual(baz.__doc__, "Whee!")
+        async with baz:
+            pass  # suppress warning
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_keywords(self):
+        # Ensure no keyword arguments are inhibited
+        @asynccontextmanager
+        async def woohoo(self, func, args, kwds):
+            yield (self, func, args, kwds)
+        async with woohoo(self=11, func=22, args=33, kwds=44) as target:
+            self.assertEqual(target, (11, 22, 33, 44))
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_recursive(self):
+        depth = 0
+        ncols = 0
+
+        @asynccontextmanager
+        async def woohoo():
+            nonlocal ncols
+            ncols += 1
+
+            nonlocal depth
+            before = depth
+            depth += 1
+            yield
+            depth -= 1
+            self.assertEqual(depth, before)
+
+        @woohoo()
+        async def recursive():
+            if depth < 10:
+                await recursive()
+
+        await recursive()
+
+        self.assertEqual(ncols, 10)
+        self.assertEqual(depth, 0)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_decorator(self):
+        entered = False
+
+        @asynccontextmanager
+        async def context():
+            nonlocal entered
+            entered = True
+            yield
+            entered = False
+
+        @context()
+        async def test():
+            self.assertTrue(entered)
+
+        self.assertFalse(entered)
+        await test()
+        self.assertFalse(entered)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_decorator_with_exception(self):
+        entered = False
+
+        @asynccontextmanager
+        async def context():
+            nonlocal entered
+            try:
+                entered = True
+                yield
+            finally:
+                entered = False
+
+        @context()
+        async def test():
+            self.assertTrue(entered)
+            raise NameError('foo')
+
+        self.assertFalse(entered)
+        with self.assertRaisesRegex(NameError, 'foo'):
+            await test()
+        self.assertFalse(entered)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_decorating_method(self):
+
+        @asynccontextmanager
+        async def context():
+            yield
+
+
+        class Test(object):
+
+            @context()
+            async 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()
+        await test.method(1, 2)
+        self.assertEqual(test.a, 1)
+        self.assertEqual(test.b, 2)
+        self.assertEqual(test.c, None)
+
+        test = Test()
+        await test.method('a', 'b', 'c')
+        self.assertEqual(test.a, 'a')
+        self.assertEqual(test.b, 'b')
+        self.assertEqual(test.c, 'c')
+
+        test = Test()
+        await test.method(a=1, b=2)
+        self.assertEqual(test.a, 1)
+        self.assertEqual(test.b, 2)
+
+
+class AclosingTestCase(unittest.IsolatedAsyncioTestCase):
+
+    @support.requires_docstrings
+    def test_instance_docs(self):
+        cm_docstring = aclosing.__doc__
+        obj = aclosing(None)
+        self.assertEqual(obj.__doc__, cm_docstring)
+
+    async def test_aclosing(self):
+        state = []
+        class C:
+            async def aclose(self):
+                state.append(1)
+        x = C()
+        self.assertEqual(state, [])
+        async with aclosing(x) as y:
+            self.assertEqual(x, y)
+        self.assertEqual(state, [1])
+
+    async def test_aclosing_error(self):
+        state = []
+        class C:
+            async def aclose(self):
+                state.append(1)
+        x = C()
+        self.assertEqual(state, [])
+        with self.assertRaises(ZeroDivisionError):
+            async with aclosing(x) as y:
+                self.assertEqual(x, y)
+                1 / 0
+        self.assertEqual(state, [1])
+
+    async def test_aclosing_bpo41229(self):
+        state = []
+
+        @contextmanager
+        def sync_resource():
+            try:
+                yield
+            finally:
+                state.append(1)
+
+        async def agenfunc():
+            with sync_resource():
+                yield -1
+                yield -2
+
+        x = agenfunc()
+        self.assertEqual(state, [])
+        with self.assertRaises(ZeroDivisionError):
+            async with aclosing(x) as y:
+                self.assertEqual(x, y)
+                self.assertEqual(-1, await x.__anext__())
+                1 / 0
+        self.assertEqual(state, [1])
+
+
+class TestAsyncExitStack(TestBaseExitStack, unittest.IsolatedAsyncioTestCase):
+    class SyncAsyncExitStack(AsyncExitStack):
+        @staticmethod
+        def run_coroutine(coro):
+            loop = asyncio.get_event_loop_policy().get_event_loop()
+            t = loop.create_task(coro)
+            t.add_done_callback(lambda f: loop.stop())
+            loop.run_forever()
+
+            exc = t.exception()
+            if not exc:
+                return t.result()
+            else:
+                context = exc.__context__
+
+                try:
+                    raise exc
+                except:
+                    exc.__context__ = context
+                    raise exc
+
+        def close(self):
+            return self.run_coroutine(self.aclose())
+
+        def __enter__(self):
+            return self.run_coroutine(self.__aenter__())
+
+        def __exit__(self, *exc_details):
+            return self.run_coroutine(self.__aexit__(*exc_details))
+
+    exit_stack = SyncAsyncExitStack
+    callback_error_internal_frames = [
+        ('__exit__', 'return self.run_coroutine(self.__aexit__(*exc_details))'),
+        ('run_coroutine', 'raise exc'),
+        ('run_coroutine', 'raise exc'),
+        ('__aexit__', 'raise exc'),
+        ('__aexit__', 'cb_suppress = cb(*exc_details)'),
+    ]
+
+    async def test_async_callback(self):
+        expected = [
+            ((), {}),
+            ((1,), {}),
+            ((1,2), {}),
+            ((), dict(example=1)),
+            ((1,), dict(example=1)),
+            ((1,2), dict(example=1)),
+        ]
+        result = []
+        async def _exit(*args, **kwds):
+            """Test metadata propagation"""
+            result.append((args, kwds))
+
+        async with AsyncExitStack() as stack:
+            for args, kwds in reversed(expected):
+                if args and kwds:
+                    f = stack.push_async_callback(_exit, *args, **kwds)
+                elif args:
+                    f = stack.push_async_callback(_exit, *args)
+                elif kwds:
+                    f = stack.push_async_callback(_exit, **kwds)
+                else:
+                    f = stack.push_async_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 = []
+        async with AsyncExitStack() as stack:
+            with self.assertRaises(TypeError):
+                stack.push_async_callback(arg=1)
+            with self.assertRaises(TypeError):
+                self.exit_stack.push_async_callback(arg=2)
+            with self.assertRaises(TypeError):
+                stack.push_async_callback(callback=_exit, arg=3)
+        self.assertEqual(result, [])
+
+    async def test_async_push(self):
+        exc_raised = ZeroDivisionError
+        async def _expect_exc(exc_type, exc, exc_tb):
+            self.assertIs(exc_type, exc_raised)
+        async def _suppress_exc(*exc_details):
+            return True
+        async 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
+            async def __aenter__(self):
+                self.fail("Should not be called!")
+            async def __aexit__(self, *exc_details):
+                await self.check_exc(*exc_details)
+
+        async with self.exit_stack() as stack:
+            stack.push_async_exit(_expect_ok)
+            self.assertIs(stack._exit_callbacks[-1][1], _expect_ok)
+            cm = ExitCM(_expect_ok)
+            stack.push_async_exit(cm)
+            self.assertIs(stack._exit_callbacks[-1][1].__self__, cm)
+            stack.push_async_exit(_suppress_exc)
+            self.assertIs(stack._exit_callbacks[-1][1], _suppress_exc)
+            cm = ExitCM(_expect_exc)
+            stack.push_async_exit(cm)
+            self.assertIs(stack._exit_callbacks[-1][1].__self__, cm)
+            stack.push_async_exit(_expect_exc)
+            self.assertIs(stack._exit_callbacks[-1][1], _expect_exc)
+            stack.push_async_exit(_expect_exc)
+            self.assertIs(stack._exit_callbacks[-1][1], _expect_exc)
+            1/0
+
+    async def test_enter_async_context(self):
+        class TestCM(object):
+            async def __aenter__(self):
+                result.append(1)
+            async def __aexit__(self, *exc_details):
+                result.append(3)
+
+        result = []
+        cm = TestCM()
+
+        async with AsyncExitStack() as stack:
+            @stack.push_async_callback  # Registered first => cleaned up last
+            async def _exit():
+                result.append(4)
+            self.assertIsNotNone(_exit)
+            await stack.enter_async_context(cm)
+            self.assertIs(stack._exit_callbacks[-1][1].__self__, cm)
+            result.append(2)
+
+        self.assertEqual(result, [1, 2, 3, 4])
+
+    async def test_enter_async_context_errors(self):
+        class LacksEnterAndExit:
+            pass
+        class LacksEnter:
+            async def __aexit__(self, *exc_info):
+                pass
+        class LacksExit:
+            async def __aenter__(self):
+                pass
+
+        async with self.exit_stack() as stack:
+            with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+                await stack.enter_async_context(LacksEnterAndExit())
+            with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+                await stack.enter_async_context(LacksEnter())
+            with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+                await stack.enter_async_context(LacksExit())
+            self.assertFalse(stack._exit_callbacks)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_async_exit_exception_chaining(self):
+        # Ensure exception chaining matches the reference behaviour
+        async def raise_exc(exc):
+            raise exc
+
+        saved_details = None
+        async def suppress_exc(*exc_details):
+            nonlocal saved_details
+            saved_details = exc_details
+            return True
+
+        try:
+            async with self.exit_stack() as stack:
+                stack.push_async_callback(raise_exc, IndexError)
+                stack.push_async_callback(raise_exc, KeyError)
+                stack.push_async_callback(raise_exc, AttributeError)
+                stack.push_async_exit(suppress_exc)
+                stack.push_async_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)
+
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    async def test_async_exit_exception_explicit_none_context(self):
+        # Ensure AsyncExitStack chaining matches actual nested `with` statements
+        # regarding explicit __context__ = None.
+
+        class MyException(Exception):
+            pass
+
+        @asynccontextmanager
+        async def my_cm():
+            try:
+                yield
+            except BaseException:
+                exc = MyException()
+                try:
+                    raise exc
+                finally:
+                    exc.__context__ = None
+
+        @asynccontextmanager
+        async def my_cm_with_exit_stack():
+            async with self.exit_stack() as stack:
+                await stack.enter_async_context(my_cm())
+                yield stack
+
+        for cm in (my_cm, my_cm_with_exit_stack):
+            with self.subTest():
+                try:
+                    async with cm():
+                        raise IndexError()
+                except MyException as exc:
+                    self.assertIsNone(exc.__context__)
+                else:
+                    self.fail("Expected IndexError, but no exception was raised")
+
+    async def test_instance_bypass_async(self):
+        class Example(object): pass
+        cm = Example()
+        cm.__aenter__ = object()
+        cm.__aexit__ = object()
+        stack = self.exit_stack()
+        with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+            await stack.enter_async_context(cm)
+        stack.push_async_exit(cm)
+        self.assertIs(stack._exit_callbacks[-1][1], cm)
+
+
+class TestAsyncNullcontext(unittest.IsolatedAsyncioTestCase):
+    async def test_async_nullcontext(self):
+        class C:
+            pass
+        c = C()
+        async with nullcontext(c) as c_in:
+            self.assertIs(c_in, c)
+
+
+if __name__ == '__main__':
+    unittest.main()