Add only_not_asyncio.

conftest.py

@@ -55,5 +55,11 @@ def only_asyncio(request, reactor_pytest):
         pytest.skip('This test is only run with --reactor=asyncio')
 
 
+@pytest.fixture(autouse=True)
+def only_not_asyncio(request, reactor_pytest):
+    if request.node.get_closest_marker('only_not_asyncio') and reactor_pytest == 'asyncio':
+        pytest.skip('This test is only run without --reactor=asyncio')
+
+
 # Generate localhost certificate files, needed by some tests
 generate_keys()

pytest.ini

@@ -21,6 +21,7 @@ addopts =
 twisted = 1
 markers =
     only_asyncio: marks tests as only enabled when --reactor=asyncio is passed
+    only_not_asyncio: marks tests as only enabled when --reactor=asyncio is not passed
 flake8-max-line-length = 119
 flake8-ignore =
     W503