class MockMenuBlockDeriver

class MockMenuBlockDeriver implements DeriverInterface {
  use StringTranslationTrait;
  
  /**
   * {@inheritdoc}
   */
  public function getDerivativeDefinition($derivative_id, $base_plugin_definition) {
    $derivatives = $this->getDerivativeDefinitions($base_plugin_definition);
    if (isset($derivatives[$derivative_id])) {
      return $derivatives[$derivative_id];
    }
    return NULL;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getDerivativeDefinitions($base_plugin_definition) {
    // This isn't strictly necessary, but it helps reduce clutter in
    // DerivativePluginTest::testDerivativeDecorator()'s $expected variable.
    // Since derivative definitions don't need further deriving, we remove this
    // key from the returned definitions.
    unset($base_plugin_definition['deriver']);
    // Here, we create some mock menu block definitions for menus that might
    // exist in a typical Drupal site. In a real implementation, we would query
    // Drupal's configuration to find out which menus actually exist.
    $derivatives = [
      'main_menu' => [
        'label' => $this->t('Main menu'),
      ] + $base_plugin_definition,
      'navigation' => [
        'label' => $this->t('Navigation'),
      ] + $base_plugin_definition,
      'foo' => [
        // Instead of the derivative label, the specific label will be used.
'label' => $this->t('Derivative label'),
        // This setting will be merged in.
'setting' => 'default',
      ] + $base_plugin_definition,
    ];
    return $derivatives;
  }

}