class DefaultsTestPluginManager

class DefaultsTestPluginManager extends DefaultPluginManager {
  
  /**
   * Constructs a new DefaultsTestPluginManager instance.
   *
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   The module handler.
   */
  public function __construct(ModuleHandlerInterface $module_handler) {
    // Create the object that can be used to return definitions for all the
    // plugins available for this type. Most real plugin managers use a richer
    // discovery implementation, but StaticDiscovery lets us add some simple
    // mock plugins for unit testing.
    $this->discovery = new StaticDiscovery();
    $this->factory = new DefaultFactory($this, 'Drupal\\Component\\Plugin\\PluginInspectionInterface');
    $this->moduleHandler = $module_handler;
    // Specify default values.
    $this->defaults = [
      'metadata' => [
        'default' => TRUE,
      ],
    ];
    // Add a plugin with a custom value.
    $this->discovery
      ->setDefinition('test_block1', [
      'class' => 'Drupal\\plugin_test\\Plugin\\plugin_test\\mock_block\\MockTestBlock',
      'metadata' => [
        'custom' => TRUE,
      ],
    ]);
    // Add a plugin that overrides the default value.
    $this->discovery
      ->setDefinition('test_block2', [
      'class' => 'Drupal\\plugin_test\\Plugin\\plugin_test\\mock_block\\MockTestBlock',
      'metadata' => [
        'custom' => TRUE,
        'default' => FALSE,
      ],
    ]);
  }

}