Updating custom module
When you edit an installed and enabled module, Drupal will not notice you added new hooks, since the list of the hooks implemented by a module is cached from Drupal. In order to make Drupal notice you edited the module and added new hooks, you need to disable and re-enable the module, without uninstalling it.

The reason why this is necessary is that module_implements(), the function that returns TRUE when a module implements a hook, contains the following code.

  // Fetch implementations from cache.
  if (empty($implementations)) {
    $implementations = cache_get('module_implements', 'cache_bootstrap');
    if ($implementations === FALSE) {
      $implementations = array();
    }
    else {
      $implementations = $implementations-&gt;data;
    }
  }