added test

Author: daniel-sanche

tests/crypt/test__python_rsa.py

@@ -191,3 +191,12 @@ def test_from_service_account_file(self):
 
         assert signer.key_id == SERVICE_ACCOUNT_INFO[base._JSON_FILE_PRIVATE_KEY_ID]
         assert isinstance(signer._key, rsa.key.PrivateKey)
+
+
+class TestModule(object):
+    def test_import_warning(self):
+        import importlib
+        from google.auth.crypt import _python_rsa
+
+        with pytest.warns(FutureWarning, match="The 'rsa' library is deprecated"):
+            importlib.reload(_python_rsa)