Defines a plugin bag which uses fruit plugins.
Expanded class hierarchy of TestPluginBag
class TestPluginBag extends PluginBag {
  /**
   * Stores the plugin manager used by this bag.
   *
   * @var \Drupal\Component\Plugin\PluginManagerInterface
   */
  protected $manager;
  /**
   * Constructs a TestPluginBag object.
   *
   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
   *   The plugin manager that handles test plugins.
   */
  public function __construct(PluginManagerInterface $manager) {
    $this->manager = $manager;
    $this->instanceIDs = drupal_map_assoc(array_keys($this->manager
      ->getDefinitions()));
  }
  /**
   * Implements \Drupal\Component\Plugin\PluginBag::initializePlugin().
   */
  protected function initializePlugin($instance_id) {
    // If the plugin was initialized before, just return.
    if (isset($this->pluginInstances[$instance_id])) {
      return;
    }
    $this->pluginInstances[$instance_id] = $this->manager
      ->createInstance($instance_id, array());
  }
}| Name   | Modifiers | Type | Description | Overrides | 
|---|---|---|---|---|
| PluginBag:: | protected | property | Stores the IDs of all potential plugin instances. | |
| PluginBag:: | protected | property | Stores all instantiated plugins. | |
| PluginBag:: | public | function | Adds an instance ID to the array of available instance IDs. | |
| PluginBag:: | public | function | Clears all instantiated plugins. | 1 | 
| PluginBag:: | public | function | Implements \Countable::count(). | |
| PluginBag:: | public | function | Implements \Iterator::current(). | |
| PluginBag:: | public | function | Retrieves a plugin instance, initializing it if necessary. | |
| PluginBag:: | public | function | Returns all instance IDs. | |
| PluginBag:: | public | function | Determines if a plugin instance exists. | |
| PluginBag:: | public | function | Implements \Iterator::key(). | |
| PluginBag:: | public | function | Implements \Iterator::next(). | |
| PluginBag:: | public | function | Removes an initialized plugin. | 1 | 
| PluginBag:: | public | function | Implements \Iterator::rewind(). | |
| PluginBag:: | public | function | Stores an initialized plugin. | |
| PluginBag:: | public | function | Sets the instance IDs property. | |
| PluginBag:: | public | function | Implements \Iterator::valid(). | |
| TestPluginBag:: | protected | property | Stores the plugin manager used by this bag. | |
| TestPluginBag:: | protected | function | Implements \Drupal\Component\Plugin\PluginBag::initializePlugin(). Overrides PluginBag:: | |
| TestPluginBag:: | public | function | Constructs a TestPluginBag object. |