add unit test

Author: Keerthan Mala

rootfs/api/tests/test_pods.py

@@ -415,6 +415,8 @@ def test_scale_errors(self, mock_requests):
         body = {'web': -1}
         response = self.client.post(url, body)
         self.assertEqual(response.status_code, 400, response.data)
+        self.assertEqual(response.data, {"detail": "Invalid scaling format: "
+                                         "['Must be greater than or equal to zero']"})
 
         # scale to something other than a number
         url = "/v2/apps/{app_id}/scale".format(**locals())