This is a overview of the types of migration tests in Drupal core.

  • Source plugin tests: These are Kernel tests at core/modules/module_name/tests/src/Kernel/Plugin/migrate/source. If you are writing a source plugin tests then reading Drupal\Tests\taxonomy\Kernel\Plugin\migrate\source\d7\VocabularyTest.php and Drupal\Tests\taxonomy\Kernel\Plugin\migrate\source\d7\TermTest.php is a good place to start.

  • Process plugin tests: These can be Unit or Kernel tests. There core process plugin unit tests for the Migrate module are at core/migrate/tests/src/Unit/process. The NullCoalesceTest is a good example to start with. There core process plugin Kernel tests for the Migrate module are at core/migrate/tests/src/Kernel/process.

  • Migration tests: This name usually refers to a Kernel test of a config or content entity migration that loads a source test fixture and then runs all the dependent migrations before asserting the results. These tests use Drupal 6 and Drupal 7 database test fixtures, in the Migrate Drupal module. The tests of migration of node types, Drupal\Tests\node\Kernel\Migrate\d7\MigrateNodeTypeTest.php, is a good example to start with.

  • Migrate UI tests: These are functional tests of the Migrate UI. Currently that is the form at /upgrade. These tests use Drupal 6 and Drupal 7 database test fixtures, in the Migrate Drupal module. A test that runs the complete migration from the UI is Drupal\Tests\migrate_drupal_ui\Functional\d7\Upgrade7Test.