#11694 Avoid asyncioreactor state leak between tests (#11695)

Give each AsyncioSelectorReactor its own event loop when running the tests.

src/twisted/internet/test/reactormixins.py

@@ -18,7 +18,7 @@
 import os
 import signal
 import time
-from typing import Dict, Optional, Sequence, Type, Union
+from typing import TYPE_CHECKING, Dict, Optional, Sequence, Type, Union
 
 from zope.interface import Interface
 
@@ -30,6 +30,11 @@
 from twisted.trial.unittest import SkipTest, SynchronousTestCase
 from twisted.trial.util import DEFAULT_TIMEOUT_DURATION, acquireAttribute
 
+if TYPE_CHECKING:
+    # Only bring in this name to support the type annotation below.  We don't
+    # really want to import a reactor module this early at runtime.
+    from twisted.internet import asyncioreactor
+
 # Access private APIs.
 try:
     from twisted.internet import process as _process
@@ -153,7 +158,7 @@ class ReactorBuilder:
             ]
         )
 
-        _reactors.append("twisted.internet.asyncioreactor.AsyncioSelectorReactor")
+        _reactors.append("twisted.internet.test.reactormixins.AsyncioSelectorReactor")
 
         if platform.isMacOSX():
             _reactors.append("twisted.internet.cfreactor.CFReactor")
@@ -366,3 +371,31 @@ class testcase(cls, SynchronousTestCase):  # type: ignore[valid-type,misc]
             testcase.__qualname__ = ".".join(cls.__qualname__.split()[0:-1] + [name])
             classes[testcase.__name__] = testcase
         return classes
+
+
+def asyncioSelectorReactor(self: object) -> "asyncioreactor.AsyncioSelectorReactor":
+    """
+    Make a new asyncio reactor associated with a new event loop.
+
+    The test suite prefers this constructor because having a new event loop
+    for each reactor provides better test isolation.  The real constructor
+    prefers to re-use (or create) a global loop because of how this interacts
+    with other asyncio-based libraries and applications (though maybe it
+    shouldn't).
+
+    @param self: The L{ReactorBuilder} subclass this is being called on.  We
+        don't use this parameter but we get called with it anyway.
+    """
+    from asyncio import new_event_loop, set_event_loop
+
+    from twisted.internet import asyncioreactor
+
+    loop = new_event_loop()
+    set_event_loop(loop)
+
+    return asyncioreactor.AsyncioSelectorReactor(loop)
+
+
+# Give it an alias that makes the names of the generated test classes fit the
+# pattern.
+AsyncioSelectorReactor = asyncioSelectorReactor

src/twisted/internet/test/test_threads.py

@@ -172,20 +172,8 @@ def test_cleanUpThreadPoolEvenBeforeReactorIsRun(self):
         reactor = self.buildReactor()
         threadPoolRef = ref(reactor.getThreadPool())
         reactor.fireSystemEvent("shutdown")
-
-        if reactor.__class__.__name__ == "AsyncioSelectorReactor":
-            self.assertIsNone(reactor.threadpool)
-            # ReactorBase.__init__ sets self.crash as a 'shutdown'
-            # event, which in turn calls stop on the underlying
-            # asyncio event loop, which in turn sets a _stopping
-            # attribute on it that's only unset after an iteration of
-            # the loop.  Subsequent tests can only reuse the asyncio
-            # loop if it's allowed to run and unset that _stopping
-            # attribute.
-            self.runReactor(reactor)
-        else:
-            gc.collect()
-            self.assertIsNone(threadPoolRef())
+        gc.collect()
+        self.assertIsNone(threadPoolRef())
 
     def test_isInIOThread(self):
         """

src/twisted/internet/test/test_time.py

@@ -43,7 +43,7 @@ def eventSource(reactor, event):
 
         else:
             raise SkipTest(
-                "Do not know how to synthesize non-time event to " "stop the test"
+                "Do not know how to synthesize non-time event to stop the test"
             )
 
         # Pick a pretty big delay.