diff --git a/core/modules/system/src/Tests/Queue/QueueSerializationTest.php b/core/modules/system/tests/src/Kernel/Queue/QueueSerializationTest.php
similarity index 96%
rename from core/modules/system/src/Tests/Queue/QueueSerializationTest.php
rename to core/modules/system/tests/src/Kernel/Queue/QueueSerializationTest.php
index 4a35cce..f58b2dd 100644
--- a/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
+++ b/core/modules/system/tests/src/Kernel/Queue/QueueSerializationTest.php
@@ -4,13 +4,13 @@
  * Contains \Drupal\system\Tests\Queue\QueueSerializationTest.
  */
 
-namespace Drupal\system\Tests\Queue;
+namespace Drupal\Tests\system\Kernel\Queue;
 
 use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 use Drupal\Core\Form\FormInterface;
 use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 use Drupal\user\Entity\User;
 
 /**
diff --git a/core/modules/system/src/Tests/Render/Element/TableTest.php b/core/modules/system/tests/src/Kernel/Render/Element/TableTest.php
similarity index 99%
rename from core/modules/system/src/Tests/Render/Element/TableTest.php
rename to core/modules/system/tests/src/Kernel/Render/Element/TableTest.php
index 827b55a..706475b 100644
--- a/core/modules/system/src/Tests/Render/Element/TableTest.php
+++ b/core/modules/system/tests/src/Kernel/Render/Element/TableTest.php
@@ -5,9 +5,9 @@
  * Contains \Drupal\system\Tests\Render\Element\TableTest.
  */
 
-namespace Drupal\system\Tests\Render\Element;
+namespace Drupal\Tests\system\Kernel\Render\Element;
 
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Tests built-in table theme functions.
diff --git a/core/modules/system/src/Tests/Render/RenderCacheTest.php b/core/modules/system/tests/src/Kernel/Render/RenderCacheTest.php
similarity index 97%
rename from core/modules/system/src/Tests/Render/RenderCacheTest.php
rename to core/modules/system/tests/src/Kernel/Render/RenderCacheTest.php
index 975358c..2f299db 100644
--- a/core/modules/system/src/Tests/Render/RenderCacheTest.php
+++ b/core/modules/system/tests/src/Kernel/Render/RenderCacheTest.php
@@ -5,9 +5,9 @@
  * Contains \Drupal\system\Tests\Render\RenderCacheTest.
  */
 
-namespace Drupal\system\Tests\Render;
+namespace Drupal\Tests\system\Kernel\Render;
 
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 use Drupal\simpletest\UserCreationTrait;
 
 /**
diff --git a/core/modules/system/src/Tests/Plugin/DerivativeTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/DerivativeTest.php
similarity index 97%
rename from core/modules/system/src/Tests/Plugin/DerivativeTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/DerivativeTest.php
index 793eeee..57a633c 100644
--- a/core/modules/system/src/Tests/Plugin/DerivativeTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/DerivativeTest.php
@@ -5,7 +5,7 @@
  * Contains \Drupal\system\Tests\Plugin\DerivativeTest.
  */
 
-namespace Drupal\system\Tests\Plugin;
+namespace Drupal\KernelTests\Core\Plugin;
 
 /**
  * Tests that derivative plugins are correctly discovered.
diff --git a/core/modules/system/src/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
similarity index 94%
rename from core/modules/system/src/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
index 6cca8f5..58c095e 100644
--- a/core/modules/system/src/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
@@ -5,9 +5,10 @@
  * Contains \Drupal\system\Tests\Plugin\Discovery\AnnotatedClassDiscoveryTest.
  */
 
-namespace Drupal\system\Tests\Plugin\Discovery;
+namespace Drupal\KernelTests\Core\Plugin\Discovery;
 
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
+use Drupal\KernelTests\Core\Plugin\Discovery\DiscoveryTestBase;
 
 /**
  * Tests that plugins are correctly discovered using annotated classes.
diff --git a/core/modules/system/src/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
similarity index 92%
rename from core/modules/system/src/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
index 890329c..2ebe95c 100644
--- a/core/modules/system/src/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
@@ -5,9 +5,10 @@
  * Contains \Drupal\system\Tests\Plugin\Discovery\CustomAnnotationClassDiscoveryTest.
  */
 
-namespace Drupal\system\Tests\Plugin\Discovery;
+namespace Drupal\KernelTests\Core\Plugin\Discovery;
 
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
+use Drupal\KernelTests\Core\Plugin\Discovery\DiscoveryTestBase;
 
 /**
  * Tests that a custom annotation class is used.
diff --git a/core/modules/system/src/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
similarity index 97%
rename from core/modules/system/src/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
index 39e7caf..67d8e6e 100644
--- a/core/modules/system/src/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
@@ -5,7 +5,7 @@
  * Contains \Drupal\system\Tests\Plugin\Discovery\CustomDirectoryAnnotatedClassDiscoveryTest.
  */
 
-namespace Drupal\system\Tests\Plugin\Discovery;
+namespace Drupal\KernelTests\Core\Plugin\Discovery;
 
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
 
diff --git a/core/modules/system/src/Tests/Plugin/Discovery/DiscoveryTestBase.php b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php
similarity index 96%
rename from core/modules/system/src/Tests/Plugin/Discovery/DiscoveryTestBase.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php
index b6f5cc1..a376c06 100644
--- a/core/modules/system/src/Tests/Plugin/Discovery/DiscoveryTestBase.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php
@@ -5,10 +5,10 @@
  * Contains \Drupal\system\Tests\Plugin\Discovery\DiscoveryTestBase.
  */
 
-namespace Drupal\system\Tests\Plugin\Discovery;
+namespace Drupal\KernelTests\Core\Plugin\Discovery;
 
 use Drupal\Core\StringTranslation\TranslatableMarkup;
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Base class for plugin discovery tests.
diff --git a/core/modules/system/src/Tests/Plugin/Discovery/StaticDiscoveryTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/StaticDiscoveryTest.php
similarity index 96%
rename from core/modules/system/src/Tests/Plugin/Discovery/StaticDiscoveryTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/Discovery/StaticDiscoveryTest.php
index c527e02..2fb493f 100644
--- a/core/modules/system/src/Tests/Plugin/Discovery/StaticDiscoveryTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/StaticDiscoveryTest.php
@@ -5,7 +5,7 @@
  * Contains \Drupal\system\Tests\Plugin\Discovery\StaticDiscoveryTest.
  */
 
-namespace Drupal\system\Tests\Plugin\Discovery;
+namespace Drupal\KernelTests\Core\Plugin\Discovery;
 
 use Drupal\Component\Plugin\Discovery\StaticDiscovery;
 
diff --git a/core/modules/system/src/Tests/Plugin/FactoryTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/FactoryTest.php
similarity index 98%
rename from core/modules/system/src/Tests/Plugin/FactoryTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/FactoryTest.php
index 44cf55f..b97b234 100644
--- a/core/modules/system/src/Tests/Plugin/FactoryTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/FactoryTest.php
@@ -5,7 +5,7 @@
  * Contains \Drupal\system\Tests\Plugin\FactoryTest.
  */
 
-namespace Drupal\system\Tests\Plugin;
+namespace Drupal\KernelTests\Core\Plugin;
 
 use Drupal\Component\Plugin\Exception\ExceptionInterface;
 
diff --git a/core/modules/system/src/Tests/Plugin/InspectionTest.php b/core/tests/Drupal/KernelTests/Core/Plugin/InspectionTest.php
similarity index 97%
rename from core/modules/system/src/Tests/Plugin/InspectionTest.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/InspectionTest.php
index 69f0a7e..90985f4 100644
--- a/core/modules/system/src/Tests/Plugin/InspectionTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/InspectionTest.php
@@ -5,7 +5,7 @@
  * Contains \Drupal\system\Tests\Plugin\InspectionTest.
  */
 
-namespace Drupal\system\Tests\Plugin;
+namespace Drupal\KernelTests\Core\Plugin;
 
 /**
  * Tests that plugins implementing PluginInspectionInterface are inspectable.
diff --git a/core/modules/system/src/Tests/Plugin/PluginTestBase.php b/core/tests/Drupal/KernelTests/Core/Plugin/PluginTestBase.php
similarity index 98%
rename from core/modules/system/src/Tests/Plugin/PluginTestBase.php
rename to core/tests/Drupal/KernelTests/Core/Plugin/PluginTestBase.php
index b4d6c1d..7710056 100644
--- a/core/modules/system/src/Tests/Plugin/PluginTestBase.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/PluginTestBase.php
@@ -5,10 +5,10 @@
  * Contains \Drupal\system\Tests\Plugin\PluginTestBase.
  */
 
-namespace Drupal\system\Tests\Plugin;
+namespace Drupal\KernelTests\Core\Plugin;
 
 use Drupal\Core\Plugin\Context\ContextDefinition;
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 use Drupal\plugin_test\Plugin\TestPluginManager;
 use Drupal\plugin_test\Plugin\MockBlockManager;
 use Drupal\plugin_test\Plugin\DefaultsTestPluginManager;
diff --git a/core/modules/system/src/Tests/Queue/QueueTest.php b/core/tests/Drupal/KernelTests/Core/Queue/QueueTest.php
similarity index 97%
rename from core/modules/system/src/Tests/Queue/QueueTest.php
rename to core/tests/Drupal/KernelTests/Core/Queue/QueueTest.php
index a1ab45e..03656ae 100644
--- a/core/modules/system/src/Tests/Queue/QueueTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Queue/QueueTest.php
@@ -5,12 +5,12 @@
  * Contains \Drupal\system\Tests\Queue\QueueTest.
  */
 
-namespace Drupal\system\Tests\Queue;
+namespace Drupal\KernelTests\Core\Queue;
 
 use Drupal\Core\Database\Database;
 use Drupal\Core\Queue\DatabaseQueue;
 use Drupal\Core\Queue\Memory;
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Queues and dequeues a set of items to check the basic queue functionality.
diff --git a/core/modules/system/src/Tests/Render/ElementInfoIntegrationTest.php b/core/tests/Drupal/KernelTests/Core/Render/ElementInfoIntegrationTest.php
similarity index 94%
rename from core/modules/system/src/Tests/Render/ElementInfoIntegrationTest.php
rename to core/tests/Drupal/KernelTests/Core/Render/ElementInfoIntegrationTest.php
index 1620253..c8453ca 100644
--- a/core/modules/system/src/Tests/Render/ElementInfoIntegrationTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Render/ElementInfoIntegrationTest.php
@@ -5,9 +5,9 @@
  * Contains \Drupal\system\Tests\Render\ElementInfoIntegrationTest.
  */
 
-namespace Drupal\system\Tests\Render;
+namespace Drupal\KernelTests\Core\Render;
 
-use Drupal\simpletest\KernelTestBase;
+use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Tests the element info.