--- /dev/null
+<?php
+
+namespace Drupal\plugin_test\Plugin\plugin_test\mock_block;
+
+use Drupal\Component\Plugin\Derivative\DeriverInterface;
+
+/**
+ * Mock implementation of DeriverInterface for the mock menu block plugin.
+ *
+ * @see \Drupal\plugin_test\Plugin\MockBlockManager
+ */
+class MockMenuBlockDeriver 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']);
+
+ // 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' => t('Main menu'),
+ ] + $base_plugin_definition,
+ 'navigation' => [
+ 'label' => t('Navigation'),
+ ] + $base_plugin_definition,
+ 'foo' => [
+ // Instead of the derivative label, the specific label will be used.
+ 'label' => t('Derivative label'),
+ // This setting will be merged in.
+ 'setting' => 'default'
+ ] + $base_plugin_definition,
+ ];
+
+ return $derivatives;
+ }
+
+}