Changed error message to be more in-line with possible reasons of the problem

lms/djangoapps/api_manager/users/tests.py

@@ -377,9 +377,11 @@ class UsersApiTests(ModuleStoreTestCase):
         data = {'email': self.test_email, 'username': local_username, 'password':
                 self.test_password, 'first_name': self.test_first_name, 'last_name': self.test_last_name}
         response = self.do_post(test_uri, data)
-        response = self.do_post(test_uri, data)
+        expected_message = "Username '{username}' or email '{email}' already exists".format(
+            username=local_username, email=self.test_email
+        )
         self.assertEqual(response.status_code, 409)
-        self.assertGreater(response.data['message'], 0)
+        self.assertEqual(response.data['message'], expected_message)
         self.assertEqual(response.data['field_conflict'], 'username or email')
 
     @mock.patch.dict("student.models.settings.FEATURES", {"ENABLE_DISCUSSION_EMAIL_DIGEST": True})

lms/djangoapps/api_manager/users/views.py

@@ -325,7 +325,9 @@ class UsersList(SecureListAPIView):
         try:
             user = User.objects.create(email=email, username=username, is_staff=is_staff)
         except IntegrityError:
-            response_data['message'] = "User '%s' already exists" % (username)
+            response_data['message'] = _("Username '{username}' or email '{email}' already exists").format(
+                username=username, email=email
+            )
             response_data['field_conflict'] = "username or email"
             return Response(response_data, status=status.HTTP_409_CONFLICT)