class MockLayoutBlockDeriver

class MockLayoutBlockDeriver implements DeriverInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getDerivativeDefinition($derivative_id, $base_plugin_definition) {
        $derivatives = $this->getDerivativeDefinitions($base_plugin_definition);
        if (isset($derivatives[$derivative_id])) {
            return $derivatives[$derivative_id];
        }
    }
    
    /**
     * {@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']);
        $derivatives = [
            // Adding a NULL key signifies that the base plugin may also be used in
            // addition to the derivatives. In this case, we allow the administrator
            // to add a generic layout block to the page.
NULL => $base_plugin_definition,
            // We also allow them to add a customized one. Here, we just mock the
            // customized one, but in a real implementation, this would be fetched
            // from some \Drupal::config() object.
'foo' => [
                'label' => t('Layout Foo'),
            ] + $base_plugin_definition,
        ];
        return $derivatives;
    }

}