reverted:
--- b/src/Event/MigrateEvents.php
+++ /dev/null
@@ -1,25 +0,0 @@
-<?php
-
-namespace Drupal\migrate_tools\Event;
-
-/**
- * Defines the row preparation event for the migration system.
- *
- * @see \Drupal\migrate\Event\MigratePrepareRowEvent
- */
-final class MigrateEvents {
-
-  /**
-   * Name of the event fired when a source item is missing.
-   *
-   * This event allows modules to perform an action whenever a specific item is
-   * missing from the source. The event listener method receives a
-   * \Drupal\migrate\Event\MigrateRowDeleteEvent instance. If no other module
-   * implements a listener, the MigrateExecutable listener (with 1000 weight)
-   * does a rollback on the item by default. Any other listener (with lower
-   * weight) might take another action (think un-publishing a node) and want to
-   * call $event->stopPropagation() to prevent the rollback.
-   */
-  const MISSING_SOURCE_ITEM = 'migrate_tools.missing_source_item';
-
-}
diff -u b/src/MigrateExecutable.php b/src/MigrateExecutable.php
--- b/src/MigrateExecutable.php
+++ b/src/MigrateExecutable.php
@@ -16,7 +16,6 @@
 use Drupal\migrate\Plugin\MigrationInterface;
 use Drupal\migrate_plus\Event\MigrateEvents as MigratePlusEvents;
 use Drupal\migrate_plus\Event\MigratePrepareRowEvent;
-use Drupal\migrate_tools\Event\MigrateEvents as MigrateToolsEvents;
 
 /**
  * Defines a migrate executable class for drush.
@@ -334,7 +333,7 @@
   public function rollbackMissingItems() {
     // Only begin the rollback operation if the migration is currently idle.
     if ($this->migration->getStatus() !== MigrationInterface::STATUS_IDLE) {
-      $status = $this->migration->getStatusLabel;
+      $status = $this->migration->getStatusLabel();
       $this->message->display($this->t('Migration @id is busy with another operation: @status',
         [
           '@id' => $this->migration->id(),
@@ -379,7 +378,7 @@
       }
 
       $event = $this->getEventDispatcher()
-        ->dispatch(MigrateToolsEvents::MISSING_SOURCE_ITEM, new MigrateRowDeleteEvent($this->migration, $destination_key));
+        ->dispatch(MigratePlusEvents::MISSING_SOURCE_ITEM, new MigrateRowDeleteEvent($this->migration, $destination_key));
       if (!$event->isPropagationStopped()) {
         $this->rollbackCurrentRow();
       }
only in patch2:
unchanged:
--- /dev/null
+++ b/tests/src/Kernel/RollbackMissingMessageTest.php
@@ -0,0 +1,124 @@
+<?php
+
+namespace Drupal\Tests\migrate_tools\Kernel;
+
+use Drupal\Tests\migrate\Kernel\MigrateTestBase;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate_tools\MigrateExecutable;
+
+/**
+ * Tests that a missing source row is removed.
+ *
+ * @group migrate
+ */
+class RollbackMissingMessageTest extends MigrateTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = [
+    'field',
+    'migrate_plus',
+    'migrate_tools',
+    'taxonomy',
+    'text',
+    'user',
+  ];
+
+  /**
+   * The stub migration used in the tests.
+   *
+   * @var Drupal\migrate\Plugin\MigrationInterface
+   */
+  protected $migration;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    // We use vocabularies to demonstrate importing and rolling back
+    // configuration entities.
+    $vocabulary_data_rows = [
+      1 => ['id' => '1', 'name' => 'categories', 'weight' => '2'],
+    ];
+
+    $this->migration = $this->createMigration('import', $vocabulary_data_rows);
+  }
+
+  /**
+   * Tests rolling back configuration and content entities.
+   */
+  public function testNonSyncableSource() {
+    $this->startCollectingMessages();
+    // Rollback.
+    $rollback_executable = new MigrateExecutable($this->migration, $this);
+    $rollback_executable->rollbackMissingItems();
+
+    $messages = $this->migration->getIdMap()->getMessageIterator();
+    $count = 0;
+    foreach ($messages as $message) {
+      $count++;
+      $this->assertContains("Migration 'import' does not support rolling back items missing from the source", $message->message);
+      $this->assertEqual($message->level, MigrationInterface::MESSAGE_ERROR);
+    }
+    // There should be only the one message.
+    $this->assertEqual($count, 1);
+  }
+
+  /**
+   * Tests rolling back configuration and content entities.
+   */
+  public function testNotIdle() {
+    $this->migration->setStatus(MigrationInterface::STATUS_STOPPING);
+    $this->startCollectingMessages();
+    // Rollback.
+    $rollback_executable = new MigrateExecutable($this->migration, $this);
+    $rollback_executable->rollbackMissingItems();
+
+    $messages = $this->migration->getIdMap()->getMessageIterator();
+    $count = 0;
+    foreach ($messages as $message) {
+      $count++;
+      $this->assertContains("Migration 'import' is busy with another operation: 4", $message->message);
+      $this->assertEqual($message->level, MigrationInterface::MESSAGE_ERROR);
+    }
+    // There should be only the one message.
+    $this->assertEqual($count, 1);
+  }
+
+  /**
+   * Helper to create a vocabulary migration with given data.
+   *
+   * @param string $id
+   *   An migration id.
+   * @param array $data
+   *   Data for the embedded data source plugin for a vocabulary migration.
+   *
+   * @return \Drupal\migrate\Plugin\MigrationInterface
+   *   A vocabulary migration stub.
+   */
+  protected function createMigration($id, array $data) {
+    $ids = ['id' => ['type' => 'integer']];
+    $definition = [
+      'id' => $id,
+      'migration_tags' => ['Import and rollback test'],
+      'source' => [
+        'plugin' => 'embedded_data',
+        'data_rows' => $data,
+        'ids' => $ids,
+      ],
+      'process' => [
+        'vid' => 'id',
+        'name' => 'name',
+        'weight' => 'weight',
+      ],
+      'destination' => ['plugin' => 'entity:taxonomy_vocabulary'],
+    ];
+
+    $this->migration = \Drupal::service('plugin.manager.migration')
+      ->createStubMigration($definition);
+    return $this->migration;
+  }
+
+}