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Testing Strategies

When to Use

Ensuring media source plugin works correctly across different scenarios and preventing regressions.

Decision

Test Type Tests What Speed Dependency
Unit tests Metadata extraction logic, helper methods Fast (< 1s) None (mocked services)
Kernel tests Database operations, entity integration Medium (2-5s) Database required
Functional tests UI forms, Media Library, display Slow (10-30s) Full Drupal bootstrap

Pattern

Unit test for metadata extraction (12 lines): 

namespace Drupal\Tests\yourmodule\Unit\Plugin\media\Source;

use Drupal\Tests\UnitTestCase;
use Drupal\yourmodule\Plugin\media\Source\CustomApi;

class CustomApiTest extends UnitTestCase {
  public function testMetadataExtraction(): void {
    $source = $this->createPluginInstance();
    $media = $this->createMock(MediaInterface::class);
    $media->method('get')->willReturn($this->createSourceFieldMock('item-123'));

    $title = $source->getMetadata($media, 'title');

    $this->assertEquals('Expected Title', $title);
  }

  protected function createPluginInstance(): CustomApi {
    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
    $entity_field_manager = $this->createMock(EntityFieldManagerInterface::class);
    $field_type_manager = $this->createMock(FieldTypePluginManagerInterface::class);
    $config_factory = $this->createMock(ConfigFactoryInterface::class);

    return new CustomApi([], 'custom_api', ['id' => 'custom_api'],
      $entity_type_manager, $entity_field_manager, $field_type_manager, $config_factory);
  }
}

Kernel test for field creation (8 lines): 

namespace Drupal\Tests\yourmodule\Kernel;

use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;

class CustomApiKernelTest extends EntityKernelTestBase {
  protected static $modules = ['media', 'yourmodule'];

  public function testSourceFieldCreation(): void {
    $media_type = $this->createMediaType('custom_api');
    $source = $media_type->getSource();
    $field = $source->createSourceField($media_type);

    $this->assertInstanceOf(FieldConfigInterface::class, $field);
    $this->assertEquals('string', $field->getType());
  }
}

Common Mistakes

  • Not mocking external services → Unit tests make real API calls, fail without network
  • No test coverage for error conditions → Plugin crashes when API unavailable
  • Only testing happy path → Bugs appear when validation fails, fields missing
  • Functional tests for logic → Slow test suite, wastes CI time
  • No test for Media Library integration → Custom widgets break selection UI

WHY: - Mock external dependencies: Unit tests run in isolation; real HTTP calls make tests slow, flaky, and dependent on external services - Error condition coverage: APIs fail 1-5% of the time in production; untested error paths cause white screens - Happy path bias: Most bugs occur in edge cases (empty values, malformed URLs, missing metadata); testing only success cases misses 80% of issues - Test at right level: Unit tests for logic (fast feedback), kernel for entity operations (integration), functional for UI (user acceptance)

See Also