TestPluginManager.php

<?php

namespace Drupal\plugin_test\Plugin;

use Drupal\Component\Plugin\PluginManagerBase;
use Drupal\Component\Plugin\Discovery\StaticDiscovery;
use Drupal\Component\Plugin\Factory\DefaultFactory;

/**
 * Defines a plugin manager used by Plugin API unit tests.
 */
class TestPluginManager extends PluginManagerBase {
    public function __construct() {
        // 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();
        // A simple plugin: a mock user login block.
        $this->discovery
            ->setDefinition('user_login', [
            'label' => 'User login',
            'class' => 'Drupal\\plugin_test\\Plugin\\plugin_test\\mock_block\\MockUserLoginBlock',
        ]);
        // In addition to finding all of the plugins available for a type, a plugin
        // type must also be able to create instances of that plugin. For example, a
        // specific instance of a "User login" block, configured with a custom
        // title. To handle plugin instantiation, plugin managers can use one of the
        // factory classes included with the plugin system, or create their own.
        // DefaultFactory is a simple, general purpose factory suitable for
        // many kinds of plugin types. Factories need access to the plugin
        // definitions (e.g., since that's where the plugin's class is specified),
        // so we provide it the discovery object.
        $this->factory = new DefaultFactory($this->discovery);
    }

}