Add tests

tests/test___all__.py

@@ -0,0 +1,24 @@
+from typing import Any
+
+
+def test___all__(pytester: Any) -> None:
+    """
+    See https://github.com/aio-libs/aiohttp/issues/6197
+    """
+    pytester.makepyfile(
+        test_a="""
+        from aiohttp import *
+    """
+    )
+    result = pytester.runpytest("-vv")
+    result.assert_outcomes(passed=0, errors=0)
+
+
+def test_web___all__(pytester: Any) -> None:
+    pytester.makepyfile(
+        test_b="""
+        from aiohttp.web import *
+    """
+    )
+    result = pytester.runpytest("-vv")
+    result.assert_outcomes(passed=0, errors=0)