Testing Plugins

When to Use

Testing blocks, field types, field formatters, field widgets, views plugins, and other plugin derivatives.

Decision

Plugin type	Minimum test type	Why
Block	Kernel	Needs block manager, rendering
Field type/formatter/widget	Kernel	Needs entity/field system
Views plugin	Kernel	Needs Views, database
Condition plugin	Unit (if simple) or Kernel	Depends on context requirements

Pattern

Testing a block plugin (Kernel):

namespace Drupal\Tests\my_module\Kernel;

use Drupal\KernelTests\KernelTestBase;

class MyBlockTest extends KernelTestBase {

  protected static $modules = ['system', 'block', 'my_module'];

  public function testBlockRendering(): void {
    $plugin_manager = $this->container->get('plugin.manager.block');
    $config = ['label' => 'Test Block'];

    $block = $plugin_manager->createInstance('my_module_block', $config);
    $build = $block->build();

    $this->assertArrayHasKey('#markup', $build);
    $this->assertStringContainsString('Expected content', $build['#markup']);
  }
}

Testing a field formatter (Kernel):

namespace Drupal\Tests\my_module\Kernel;

use Drupal\entity_test\Entity\EntityTest;
use Drupal\KernelTests\KernelTestBase;

class MyFormatterTest extends KernelTestBase {

  protected static $modules = ['field', 'entity_test', 'my_module'];

  protected function setUp(): void {
    parent::setUp();
    $this->installEntitySchema('entity_test');
    // Create field instance, attach formatter
  }

  public function testFormatterOutput(): void {
    $entity = EntityTest::create(['my_field' => 'test value']);
    $display = $entity->get('my_field')->view(['type' => 'my_formatter']);

    $output = $this->container->get('renderer')->renderRoot($display);
    $this->assertStringContainsString('formatted: test value', $output);
  }
}

Testing plugin discovery (Unit):

public function testPluginAnnotation(): void {
  $plugin_manager = $this->container->get('plugin.manager.block');
  $definitions = $plugin_manager->getDefinitions();

  $this->assertArrayHasKey('my_module_block', $definitions);
  $this->assertEquals('My Block', $definitions['my_module_block']['admin_label']);
}

Reference: /core/modules/block/tests/src/Kernel/BlockViewBuilderTest.php

Common Mistakes

• Not installing required modules for plugin manager -- "Plugin manager not found"
• Testing rendering without installing entity schema -- "Table doesn't exist"
• Hardcoding plugin IDs instead of using constants -- string typos not caught
• Not testing plugin derivatives -- base plugin works but derivatives broken
• Forgetting to test access control in block plugins -- blocks visible when they shouldn't be

See Also

• Testing Services
• Testing Forms
• Reference: /core/modules/block/tests/src/Kernel/BlockViewBuilderTest.php
• Example: /core/modules/field/tests/src/Kernel/