class ConfigurableTestClass

class ConfigurableTestClass extends PluginBase implements ConfigurableInterface {
  use ConfigurableTrait {
    defaultConfiguration as traitDefaultConfiguration;
  }
  
  /**
   * A default configuration for the test class to return.
   *
   * @var array|null
   */
  protected ?array $defaultConfiguration = NULL;
  
  /**
   * {@inheritdoc}
   */
  public function __construct(array $configuration = [], string $plugin_id = '', array $plugin_definition = []) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->setConfiguration($configuration);
  }
  
  /**
   * Sets the default configuration this test will return.
   *
   * @param array $default_configuration
   *   The default configuration to use.
   */
  public function setDefaultConfiguration(array $default_configuration) : void {
    $this->defaultConfiguration = $default_configuration;
  }
  
  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() : array {
    return $this->defaultConfiguration ?? $this->traitDefaultConfiguration();
  }

}