Cmocka: how to mock a function called as a function pointer

Question

INT32 shellInit(shell_t *shell)
{
    INT32 ret = ZKOS_SUCCESS;

    /* initialize shell device */
    if (shell->dev->ops->init)
    {
        if ((ret = shell->dev->ops->init(shell->dev)) != ZKOS_SUCCESS)
        {
            ZKOS_LOG("fail to initialize shell device.\n");
            return ret;
        }
    }
    
    ...
    
    return ret;
}

As the above code shows, shellInit calls a function by a function pointer shell->dev->ops->init, which has been assigned to a function defined in another file. How to mock this called function?