Add test for verifying task cancellation

Author: Askaholic

tests/test_event_loop_cleanup.py

@@ -0,0 +1,38 @@
+from textwrap import dedent
+
+
+def test_task_canceled_on_test_end(testdir):
+    testdir.makepyfile(
+        dedent(
+            """\
+        import asyncio
+        import pytest
+
+        pytest_plugins = 'pytest_asyncio'
+
+        @pytest.mark.asyncio
+        async def test_a():
+            loop = asyncio.get_event_loop()
+
+            async def run_forever():
+                while True:
+                    await asyncio.sleep(0.1)
+
+            loop.create_task(run_forever())
+        """
+        )
+    )
+    testdir.makefile(
+        ".ini",
+        pytest=dedent(
+            """\
+        [pytest]
+        asyncio_mode = strict
+        filterwarnings =
+            error
+    """
+        ),
+    )
+    result = testdir.runpytest_subprocess()
+    result.assert_outcomes(passed=1)
+    result.stderr.no_fnmatch_line("Task was destroyed but it is pending!")