import asyncio
import contextvars
import inspect
import warnings
from .case import TestCase
class IsolatedAsyncioTestCase(TestCase):
# Names intentionally have a long prefix
# to reduce a chance of clashing with user-defined attributes
# from inherited test case
#
# The class doesn't call loop.run_until_complete(self.setUp()) and family
# but uses a different approach:
# 1. create a long-running task that reads self.setUp()
# awaitable from queue along with a future
# 2. await the awaitable object passing in and set the result
# into the future object
# 3. Outer code puts the awaitable and the future object into a queue
# with waiting for the future
# The trick is necessary because every run_until_complete() call
# creates a new task with embedded ContextVar context.
# To share contextvars between setUp(), test and tearDown() we need to execute
# them inside the same task.
# Note: the test case modifies event loop policy if the policy was not instantiated
# yet, unless loop_factory=asyncio.EventLoop is set.
# asyncio.get_event_loop_policy() creates a default policy on demand but never
# returns None
# I believe this is not an issue in user level tests but python itself for testing
# should reset a policy in every test module
# by calling asyncio.set_event_loop_policy(None) in tearDownModule()
# or set loop_factory=asyncio.EventLoop
loop_factory = None
def __init__(self, methodName='runTest'):
super().__init__(methodName)
self._asyncioRunner = None
self._asyncioTestContext = contextvars.copy_context()
async def asyncSetUp(self):
pass
async def asyncTearDown(self):
pass
def addAsyncCleanup(self, func, /, *args, **kwargs):
# A trivial trampoline to addCleanup()
# the function exists because it has a different semantics
# and signature:
# addCleanup() accepts regular functions
# but addAsyncCleanup() accepts coroutines
#
# We intentionally don't add inspect.iscoroutinefunction() check
# for func argument because there is no way
# to check for async function reliably:
# 1. It can be "async def func()" itself
# 2. Class can implement "async def __call__()" method
# 3. Regular "def func()" that returns awaitable object
self.addCleanup(*(func, *args), **kwargs)
async def enterAsyncContext(self, cm):
"""Enters the supplied asynchronous context manager.
If successful, also adds its __aexit__ method as a cleanup
function and returns the result of the __aenter__ method.
"""
# We look up the special methods on the type to match the with
# statement.
cls = type(cm)
try:
enter = cls.__aenter__
exit = cls.__aexit__
except AttributeError:
raise TypeError(f"'{cls.__module__}.{cls.__qualname__}' object does "
f"not support the asynchronous context manager protocol"
) from None
result = await enter(cm)
self.addAsyncCleanup(exit, cm, None, None, None)
return result
def _callSetUp(self):
# Force loop to be initialized and set as the current loop
# so that setUp functions can use get_event_loop() and get the
# correct loop instance.
self._asyncioRunner.get_loop()
self._asyncioTestContext.run(self.setUp)
self._callAsync(self.asyncSetUp)
def _callTestMethod(self, method):
result = self._callMaybeAsync(method)
if result is not None:
msg = (
f'It is deprecated to return a value that is not None '
f'from a test case ({method} returned {type(result).__name__!r})',
)
warnings.warn(msg, DeprecationWarning, stacklevel=4)
def _callTearDown(self):
self._callAsync(self.asyncTearDown)
self._asyncioTestContext.run(self.tearDown)
def _callCleanup(self, function, *args, **kwargs):
self._callMaybeAsync(function, *args, **kwargs)
def _callAsync(self, func, /, *args, **kwargs):
assert self._asyncioRunner is not None, 'asyncio runner is not initialized'
assert inspect.iscoroutinefunction(func), f'{func!r} is not an async function'
return self._asyncioRunner.run(
func(*args, **kwargs),
context=self._asyncioTestContext
)
def _callMaybeAsync(self, func, /, *args, **kwargs):
assert self._asyncioRunner is not None, 'asyncio runner is not initialized'
if inspect.iscoroutinefunction(func):
return self._asyncioRunner.run(
func(*args, **kwargs),
context=self._asyncioTestContext,
)
else:
return self._asyncioTestContext.run(func, *args, **kwargs)
def _setupAsyncioRunner(self):
assert self._asyncioRunner is None, 'asyncio runner is already initialized'
runner = asyncio.Runner(debug=True, loop_factory=self.loop_factory)
self._asyncioRunner = runner
def _tearDownAsyncioRunner(self):
runner = self._asyncioRunner
runner.close()
def run(self, result=None):
self._setupAsyncioRunner()
try:
return super().run(result)
finally:
self._tearDownAsyncioRunner()
def debug(self):
self._setupAsyncioRunner()
super().debug()
self._tearDownAsyncioRunner()
def __del__(self):
if self._asyncioRunner is not None:
self._tearDownAsyncioRunner()
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