add support for async contextvars

pytest_asyncio/plugin.py

@@ -4,6 +4,8 @@
 import functools
 import inspect
 import socket
+from contextvars import Context, copy_context
+from asyncio import coroutines
 
 import pytest
 try:
@@ -102,6 +104,7 @@ async def async_finalizer():
             return asyncio.get_event_loop().run_until_complete(setup())
 
         fixturedef.func = wrapper
+
     elif inspect.iscoroutinefunction(fixturedef.func):
         coro = fixturedef.func
 
@@ -154,9 +157,12 @@ def inner(**kwargs):
 
 
 def pytest_runtest_setup(item):
-    if 'asyncio' in item.keywords and 'event_loop' not in item.fixturenames:
-        # inject an event loop fixture for all async tests
-        item.fixturenames.append('event_loop')
+    if 'asyncio' in item.keywords:
+        if 'event_loop' not in item.fixturenames:
+            # inject an event loop fixture for all async tests
+            item.fixturenames.append('event_loop')
+        if 'context' not in item.fixturenames:
+            item.fixturenames.append('context')
     if item.get_closest_marker("asyncio") is not None \
         and not getattr(item.obj, 'hypothesis', False) \
         and getattr(item.obj, 'is_hypothesis_test', False):
@@ -165,6 +171,40 @@ def pytest_runtest_setup(item):
                 'only works with Hypothesis 3.64.0 or later.' % item
             )
 
+class Task(asyncio.tasks._PyTask):
+    def __init__(self, coro, *, loop=None, name=None, context=None):
+        asyncio.futures._PyFuture.__init__(self, loop=loop)
+        if self._source_traceback:
+            del self._source_traceback[-1]
+        if not coroutines.iscoroutine(coro):
+            # raise after Future.__init__(), attrs are required for __del__
+            # prevent logging for pending task in __del__
+            self._log_destroy_pending = False
+            raise TypeError(f"a coroutine was expected, got {coro!r}")
+
+        if name is None:
+            self._name = f'Task-{asyncio.tasks._task_name_counter()}'
+        else:
+            self._name = str(name)
+
+        self._must_cancel = False
+        self._fut_waiter = None
+        self._coro = coro
+        self._context = context if context is not None else copy_context()
+
+        self._loop.call_soon(self.__step, context=self._context)
+        asyncio._register_task(self)
+
+
+@pytest.fixture
+def context(event_loop, request):
+    """Create an empty context for the async test case and it's async fixtures."""
+    context = Context()
+    def taskfactory(loop, coro):
+        return Task(coro, loop=loop, context=context)
+    event_loop.set_task_factory(taskfactory)
+    return context
+
 
 @pytest.fixture
 def event_loop(request):

tests/test_contextvars.py

@@ -0,0 +1,21 @@
+"""Quick'n'dirty unit tests for provided fixtures and markers."""
+import asyncio
+import pytest
+
+import pytest_asyncio.plugin
+
+from contextvars import ContextVar
+
+
+ctxvar = ContextVar('ctxvar')
+
+
+@pytest.fixture
+async def set_some_context(context):
+    ctxvar.set('quarantine is fun')
+
+
+@pytest.mark.asyncio
+async def test_test(set_some_context):
+    # print ("Context in test:", list(context.items()))
+    assert ctxvar.get() == 'quarantine is fun'