diff --git a/core/modules/migrate/src/Tests/MigrateTestBase.php b/core/modules/migrate/src/Tests/MigrateTestBase.php
index 538db55..3b34d86 100644
--- a/core/modules/migrate/src/Tests/MigrateTestBase.php
+++ b/core/modules/migrate/src/Tests/MigrateTestBase.php
@@ -80,6 +80,7 @@ protected function setUp() {
   protected function tearDown() {
     Database::removeConnection('migrate');
     parent::tearDown();
+    unset($this->migration, $this->migrateMessages, $this->collectMessages, $this->databaseDumpFiles);
   }
 
   /**