1) Test case (test_async_fixtures_with_finalizer) refactoring to pass on python 3.6 & 3.5

2) An additional test case (test_module_with_get_event_loop_finalizer).
   Refactoring previous test case I got to another potential issue: Finalizers using get_event_loop() instead of event_loop [on a module scope fixture]
   To be able to pass this new test case I needed some additional changes on next event_loop fixture block(  https://github.com/pytest-dev/pytest-asyncio/blob/v0.12.0/pytest_asyncio/plugin.py#L54-L66):
   - This block needs to apply on all event_loop fixture scopes (so I remove 'asyncio' in request.keywords, that only apply to function scope)
   - The get_event_loop() method inside this block has following side effects (See https://github.com/python/cpython/blob/3.8/Lib/asyncio/events.py#L636):
     - As no loop is still set, then L636 is executed, and so a new event_loop (let's call it L2) is first created and then set.
	 - And then finalizer will restore L2 at the end of test. What has no sense, to restore L2 that wasn't before the test. And additionally this L2 is never closed.
	 So it seeems that get_event_loop() should be removed, and so I see no reasons for any finalizer.

3) DRY: New FixtureStripper to avoid repeating code

Author: alblasco

pytest_asyncio/plugin.py

@@ -48,43 +48,53 @@ def pytest_pycollect_makeitem(collector, name, obj):
             return list(collector._genfunctions(name, obj))
 
 
+class FixtureStripper:
+    """Include additional Fixture, and then strip them"""
+    REQUEST = "request"
+    EVENT_LOOP = "event_loop"
+
+    def __init__(self, fixturedef):
+        self.fixturedef = fixturedef
+        self.to_strip = set()
+
+    def add(self, name):
+        """Add fixture name to fixturedef
+         and record in to_strip list (If not previously included)"""
+        if name in self.fixturedef.argnames:
+            return
+        self.fixturedef.argnames += (name, )
+        self.to_strip.add(name)
+
+    def get_and_strip_from(self, name, data_dict):
+        """Strip name from data, and return value"""
+        result = data_dict[name]
+        if name in self.to_strip:
+            del data_dict[name]
+        return result
+
+
 @pytest.hookimpl(hookwrapper=True)
 def pytest_fixture_setup(fixturedef, request):
     """Adjust the event loop policy when an event loop is produced."""
-    if fixturedef.argname == "event_loop" and 'asyncio' in request.keywords:
+    if fixturedef.argname == "event_loop":
         outcome = yield
         loop = outcome.get_result()
         policy = asyncio.get_event_loop_policy()
-        try:
-            old_loop = policy.get_event_loop()
-        except RuntimeError as exc:
-            if 'no current event loop' not in str(exc):
-                raise
-            old_loop = None
         policy.set_event_loop(loop)
-        fixturedef.addfinalizer(lambda: policy.set_event_loop(old_loop))
         return
 
     if isasyncgenfunction(fixturedef.func):
         # This is an async generator function. Wrap it accordingly.
         generator = fixturedef.func
 
-        strip_event_loop = False
-        if 'event_loop' not in fixturedef.argnames:
-            fixturedef.argnames += ('event_loop', )
-            strip_event_loop = True
-        strip_request = False
-        if 'request' not in fixturedef.argnames:
-            fixturedef.argnames += ('request', )
-            strip_request = True
+        fixture_stripper = FixtureStripper(fixturedef)
+        fixture_stripper.add(FixtureStripper.EVENT_LOOP)
+        fixture_stripper.add(FixtureStripper.REQUEST)
+
 
         def wrapper(*args, **kwargs):
-            loop = kwargs['event_loop']
-            request = kwargs['request']
-            if strip_event_loop:
-                del kwargs['event_loop']
-            if strip_request:
-                del kwargs['request']
+            loop = fixture_stripper.get_and_strip_from(FixtureStripper.EVENT_LOOP, kwargs)
+            request = fixture_stripper.get_and_strip_from(FixtureStripper.REQUEST, kwargs)
 
             gen_obj = generator(*args, **kwargs)
 
@@ -112,15 +122,11 @@ async def async_finalizer():
     elif inspect.iscoroutinefunction(fixturedef.func):
         coro = fixturedef.func
 
-        strip_event_loop = False
-        if 'event_loop' not in fixturedef.argnames:
-            fixturedef.argnames += ('event_loop', )
-            strip_event_loop = True
+        fixture_stripper = FixtureStripper(fixturedef)
+        fixture_stripper.add(FixtureStripper.EVENT_LOOP)
 
         def wrapper(*args, **kwargs):
-            loop = kwargs['event_loop']
-            if strip_event_loop:
-                del kwargs['event_loop']
+            loop = fixture_stripper.get_and_strip_from(FixtureStripper.EVENT_LOOP, kwargs)
 
             async def setup():
                 res = await coro(*args, **kwargs)

tests/async_fixtures/test_async_fixtures_with_finalizer.py

@@ -0,0 +1,51 @@
+import asyncio
+import contextlib
+import functools
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_module_with_event_loop_finalizer(port1):
+    await asyncio.sleep(0.01)
+    assert port1
+
+@pytest.mark.asyncio
+async def test_module_with_get_event_loop_finalizer(port2):
+    await asyncio.sleep(0.01)
+    assert port2
+
+@pytest.fixture(scope="module")
+def event_loop():
+    """Change event_loop fixture to module level."""
+    policy = asyncio.get_event_loop_policy()
+    loop = policy.new_event_loop()
+    yield loop
+    loop.close()
+
+
+@pytest.fixture(scope="module")
+async def port1(request, event_loop):
+    def port_finalizer(finalizer):
+        async def port_afinalizer():
+            # await task inside get_event_loop()
+            # RantimeError is raised if task is created on a different loop
+            await finalizer
+        event_loop.run_until_complete(port_afinalizer())
+
+    worker = asyncio.create_task(asyncio.sleep(0.2))
+    request.addfinalizer(functools.partial(port_finalizer, worker))
+    return True
+
+
+@pytest.fixture(scope="module")
+async def port2(request, event_loop):
+    def port_finalizer(finalizer):
+        async def port_afinalizer():
+            # await task inside get_event_loop()
+            # if loop is different a RuntimeError is raised
+            await finalizer
+        asyncio.get_event_loop().run_until_complete(port_afinalizer())
+
+    worker = asyncio.create_task(asyncio.sleep(0.2))
+    request.addfinalizer(functools.partial(port_finalizer, worker))
+    return True