Merge pull request #9917 from nathanielmanistaatgoogle/missing-main

Add missing unittest.main call.
diff --git a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
index f2e3898..ee23503 100644
--- a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
+++ b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
@@ -249,3 +249,7 @@
         with self.assertRaises(grpc.RpcError):
             for _ in range(test_constants.STREAM_LENGTH // 2 + 1):
                 next(response_iterator)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)