Fix test on py3.7 and pytest 6.1.0

Author: asvetlov

tests/test_simple.py

@@ -257,7 +257,18 @@ def test_a():
         """
         )
     )
-    result = testdir.runpytest_subprocess("--asyncio-mode=strict")
+    testdir.makefile(
+        ".ini",
+        pytest=dedent(
+            """\
+        [pytest]
+        asyncio_mode = strict
+        filterwarnings =
+            default
+    """
+        ),
+    )
+    result = testdir.runpytest_subprocess()
     result.assert_outcomes(passed=1)
     result.stdout.fnmatch_lines(
         ["*is marked with '@pytest.mark.asyncio' but it is not an async function.*"]