    @Test
    public void testExisting() throws RepositoryException {

        CreateGroupOperation createGroupOperation = new CreateGroupOperation();
        PostResponse response = new JSONResponse();

        context.currentResource("/home/users");
        context.request().setParameterMap(
                ImmutableMap.<String, Object>builder().put(SlingPostConstants.RP_NODE_NAME, "test5").build());

        UserManager userManager = CommonUtils.getUserManager(context.resourceResolver());
        Mockito.when(userManager.getAuthorizable(Mockito.any(Principal.class))).thenReturn(Mockito.mock(Group.class));

        createGroupOperation.run(context.request(), response, null);

        assertNotNull(response.getError());
    }