diff -u b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php
--- b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php
+++ b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php
@@ -8,7 +8,7 @@
 use Drupal\migrate\Row;
 
 /**
- * Base class for unit tests of Migrate source plugins.
+ * Base class for tests of Migrate source plugins.
  */
 abstract class MigrateSourceTestBase extends KernelTestBase {
 
@@ -74,14 +74,6 @@
   }
 
   /**
-   * {@inheritdoc}
-   */
-  protected function tearDown() {
-    parent::tearDown();
-    $this->plugin = NULL;
-  }
-
-  /**
    * Determines the plugin to be tested by reading the class @covers annotation.
    *
    * @return string
@@ -165,7 +157,7 @@
     }
 
     $i = 0;
-    /** @var Row $row */
+    /** @var \Drupal\migrate\Row $row */
     foreach ($plugin as $row) {
       $this->assertInstanceOf(Row::class, $row);
 
diff -u b/core/modules/migrate/tests/src/Kernel/MigrateSqlSourceTestBase.php b/core/modules/migrate/tests/src/Kernel/MigrateSqlSourceTestBase.php
--- b/core/modules/migrate/tests/src/Kernel/MigrateSqlSourceTestBase.php
+++ b/core/modules/migrate/tests/src/Kernel/MigrateSqlSourceTestBase.php
@@ -5,7 +5,7 @@
 use Drupal\Core\Database\Driver\sqlite\Connection;
 
 /**
- * Base class for unit tests of Migrate source plugins that use a database.
+ * Base class for tests of Migrate source plugins that use a database.
  */
 abstract class MigrateSqlSourceTestBase extends MigrateSourceTestBase {