Issue #2797421 by dcam, mikeryan, chx, id.conky, mkalkbrenner, mikelutz:...

    /** @var \Drupal\Component\Plugin\PluginManagerInterface $source_plugin_manager */

    $source_plugin_manager = \Drupal::service('plugin.manager.migrate.source');

    return array_filter($this->decorated->getDefinitions(), function (array $definition) use ($source_plugin_manager) {

      return $source_plugin_manager->hasDefinition($definition['source']['plugin']);

      return !empty($definition['source']['plugin']) && $source_plugin_manager->hasDefinition($definition['source']['plugin']);

    });

  }

<?php

declare(strict_types=1);

namespace Drupal\Tests\migrate\Unit\Plugin;

use Drupal\Component\Plugin\Discovery\DiscoveryInterface;

use Drupal\Core\DependencyInjection\ContainerBuilder;

use Drupal\migrate\Plugin\MigrateSourcePluginManager;

use Drupal\migrate\Plugin\NoSourcePluginDecorator;

use Drupal\Tests\UnitTestCase;

/**

 * @coversDefaultClass \Drupal\migrate\Plugin\NoSourcePluginDecorator

 * @group migrate

 */

class NoSourcePluginDecoratorTest extends UnitTestCase {

  /**

   * @covers ::getDefinitions

   * @dataProvider providerGetDefinitions

   */

  public function testGetDefinitions(array $definition, bool $source_exists): void {

    $source_manager = $this->createMock(MigrateSourcePluginManager::class);

    $source_manager->expects($this->any())

      ->method('hasDefinition')

      ->willReturn($source_exists);

    $container = new ContainerBuilder();

    $container->set('plugin.manager.migrate.source', $source_manager);

    \Drupal::setContainer($container);

    $discovery_interface = $this->createMock(DiscoveryInterface::class);

    $discovery_interface->expects($this->once())

      ->method('getDefinitions')

      ->willReturn([$definition]);

    $decorator = new NoSourcePluginDecorator($discovery_interface);

    $results = $decorator->getDefinitions();

    if ($source_exists) {

      $this->assertEquals([$definition], $results);

    }

    else {

      $this->assertEquals([], $results);

    }

  }

  /**

   * Provides data for testGetDefinitions().

   */

  public static function providerGetDefinitions(): array {

    return [

      'source exists' => [

        [

          'source' => ['plugin' => 'valid_plugin'],

          'process' => [],

          'destination' => [],

        ],

        TRUE,

      ],

      'source does not exist' => [

        [

          'source' => ['plugin' => 'invalid_plugin'],

          'process' => [],

          'destination' => [],

        ],

        FALSE,

      ],

      'source is not defined' => [

        [

          'process' => [],

          'destination' => [],

        ],

        FALSE,

      ],

    ];

  }

}