class ModuleImplementsAlterTest

class ModuleImplementsAlterTest extends KernelTestBase {
  
  /**
   * {@inheritdoc}
   */
  protected static $modules = [
    'system',
  ];
  
  /**
   * Tests hook_module_implements_alter() adding an implementation.
   *
   * @see \Drupal\Core\Extension\ModuleHandler::buildImplementationInfo()
   * @see module_test_module_implements_alter()
   */
  public function testModuleImplementsAlter() {
    // Get an instance of the module handler, to observe how it is going to be
    // replaced.
    $module_handler = \Drupal::moduleHandler();
    $this->assertSame(\Drupal::moduleHandler(), $module_handler, 'Module handler instance is still the same.');
    // Install the module_test module.
    \Drupal::service('module_installer')->install([
      'module_test',
    ]);
    // Assert that the \Drupal::moduleHandler() instance has been replaced.
    $this->assertNotSame(\Drupal::moduleHandler(), $module_handler, 'The \\Drupal::moduleHandler() instance has been replaced during \\Drupal::moduleHandler()->install().');
    // Assert that module_test.module is now included.
    $this->assertTrue(function_exists('module_test_modules_installed'), 'The file module_test.module was successfully included.');
    $this->assertArrayHasKey('module_test', \Drupal::moduleHandler()->getModuleList());
    $this->assertTrue(\Drupal::moduleHandler()->hasImplementations('modules_installed', 'module_test'), 'module_test implements hook_modules_installed().');
    $this->assertTrue(\Drupal::moduleHandler()->hasImplementations('module_implements_alter', 'module_test'), 'module_test implements hook_module_implements_alter().');
    // Assert that module_test.implementations.inc is not included yet.
    $this->assertFalse(function_exists('module_test_altered_test_hook'), 'The file module_test.implementations.inc is not included yet.');
    // Trigger hook discovery for hook_altered_test_hook().
    // Assert that module_test_module_implements_alter(*, 'altered_test_hook')
    // has added an implementation.
    $this->assertTrue(\Drupal::moduleHandler()->hasImplementations('altered_test_hook', 'module_test'), 'module_test implements hook_altered_test_hook().');
    // Assert that module_test.implementations.inc was included as part of the process.
    $this->assertTrue(function_exists('module_test_altered_test_hook'), 'The file module_test.implementations.inc was included.');
  }
  
  /**
   * Tests adding a non-existing function to hook_module_implements_alter().
   *
   * @see \Drupal\Core\Extension\ModuleHandler::buildImplementationInfo()
   * @see module_test_module_implements_alter()
   */
  public function testModuleImplementsAlterNonExistingImplementation() {
    // Install the module_test module.
    \Drupal::service('module_installer')->install([
      'module_test',
    ]);
    // Trigger hook discovery.
    $this->expectException(\RuntimeException::class);
    $this->expectExceptionMessage('An invalid implementation module_test_unimplemented_test_hook was added by hook_module_implements_alter()');
    \Drupal::moduleHandler()->hasImplementations('unimplemented_test_hook');
  }

}