Drupal migrate dry run

dry_run.php

<?php

use Drupal\migrate_plus\Event\MigrateEvents as MigratePlusEvents;
use Drupal\migrate_plus\Event\MigratePrepareRowEvent;
use Drupal\migrate\Plugin\MigrateIdMapInterface;

function dry_run_migration($migration_id) {
  // Get the migration source.
  $migrationManager = \Drupal::service('plugin.manager.config_entity_migration');
  $migration = $migrationManager->createInstance($migration_id);
  $source = $migration->getSourcePlugin();

  // Usually, the source will automatically skip rows that haven't changed,
  // since we don't have to do anything with them.
  // But to detect deletions, we need to see every single row--so we mark each
  // row as 'changed', to make sure they're not skipped.
  $dispatcher = \Drupal::service('event_dispatcher');
  $dispatcher->addListener(MigratePlusEvents::PREPARE_ROW,
    function(MigratePrepareRowEvent $event) {
      $row = $event->getRow();
      if ($row->getIdMap()) {
        $row->setIdMap([
            'source_row_status' => MigrateIdMapInterface::STATUS_NEEDS_UPDATE
          ] + $row->getIdMap());
      }
    }
  );

  // Look at each row to see if it's new or updated.
  $seen = [];
  foreach ($source as $row) {
    $ids = implode(', ', array_values($row->getSourceIdValues()));
    if (empty($row->getIdMap()['original_hash'])) {
      printf("NEW: $ids\n");
    }
    elseif ($row->changed()) {
      printf("UPDATED: $ids\n");
    }
    // Mark this row as seen.
    $seen[$ids] = TRUE;
  }

  // Anything that we previously migrated, but wasn't in our source,
  // must have been deleted.
  $id_map = $migration->getIdMap();
  foreach ($migration->getIdMap() as $row) {
    if (empty($id_map->currentDestination())) {
      // When previously processing this row, nothing was imported.
      continue;
    }

    $ids = implode(', ', array_values($id_map->currentSource()));
    if (empty($seen[$ids])) {
      printf("DELETED: $ids\n");
    }
  }
}

dry_run_migration('my_test_migration');