Remove unwanted side-effect in test_oauth2client introduced by #196

tests/test_oauth2client.py

@@ -583,9 +583,15 @@ class BasicCredentialsTests(unittest.TestCase):
         user_agent, revoke_uri=GOOGLE_REVOKE_URI)
 
     # Provoke a failure if @util.positional is not respected.
+    self.old_positional_enforcement = (
+        oauth2client_util.positional_parameters_enforcement)
     oauth2client_util.positional_parameters_enforcement = (
         oauth2client_util.POSITIONAL_EXCEPTION)
 
+  def tearDown(self):
+    oauth2client_util.positional_parameters_enforcement = (
+        self.old_positional_enforcement)
+
   def test_token_refresh_success(self):
     for status_code in REFRESH_STATUS_CODES:
       token_response = {'access_token': '1/3w', 'expires_in': 3600}