add unit test for delete_group_user method

add unit test for delete_group_user method

Change-Id: I5566c6b5300ff47d37f3dbb224e5e7ba83a49c57
diff --git a/tempest/tests/lib/services/identity/v3/test_groups_client.py b/tempest/tests/lib/services/identity/v3/test_groups_client.py
index 38cf3ae..e3c9851 100644
--- a/tempest/tests/lib/services/identity/v3/test_groups_client.py
+++ b/tempest/tests/lib/services/identity/v3/test_groups_client.py
@@ -211,3 +211,13 @@
             group_id='6e13e2068cf9466e98950595baf6bb35',
             user_id='642688fa65a84217b86cef3c063de2b9',
         )
+
+    def test_delete_group_user(self):
+        self.check_service_client_function(
+            self.client.delete_group_user,
+            'tempest.lib.common.rest_client.RestClient.delete',
+            {},
+            status=204,
+            group_id='6e13e2068cf9466e98950595baf6bb35',
+            user_id='642688fa65a84217b86cef3c063de2b9',
+        )