diff --git a/composer.json b/composer.json
index d3dc1db511..d3fc07b70a 100644
--- a/composer.json
+++ b/composer.json
@@ -55,7 +55,8 @@
     },
     "autoload": {
         "psr-4": {
-            "Drupal\\Core\\Composer\\": "core/lib/Drupal/Core/Composer"
+            "Drupal\\Core\\Composer\\": "core/lib/Drupal/Core/Composer",
+            "Drupal\\Tool\\": "core/tools"
         }
     },
     "autoload-dev": {
diff --git a/core/modules/file/tests/src/Functional/FileFieldTestBase.php b/core/modules/file/tests/src/Functional/FileFieldTestBase.php
index 7fa558bd51..a3552f8685 100644
--- a/core/modules/file/tests/src/Functional/FileFieldTestBase.php
+++ b/core/modules/file/tests/src/Functional/FileFieldTestBase.php
@@ -3,7 +3,7 @@
 namespace Drupal\Tests\file\Functional;
 
 use Drupal\Component\Render\FormattableMarkup;
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\file\FileInterface;
@@ -15,7 +15,7 @@
 // dynamically load a compatibility trait dependent on the PHPUnit runner
 // version.
 if (!trait_exists(PhpunitVersionDependentFileFieldTestBaseTrait::class, FALSE)) {
-  class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\FileFieldTestBaseTrait", PhpunitVersionDependentFileFieldTestBaseTrait::class);
+  class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\FileFieldTestBaseTrait", PhpunitVersionDependentFileFieldTestBaseTrait::class);
 }
 
 /**
diff --git a/core/modules/file/tests/src/Functional/FileFieldValidateTest.php b/core/modules/file/tests/src/Functional/FileFieldValidateTest.php
index 8af0f85ae0..6cae2c16a1 100644
--- a/core/modules/file/tests/src/Functional/FileFieldValidateTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldValidateTest.php
@@ -4,7 +4,7 @@
 
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\file\Entity\File;
 use Drupal\Tests\Traits\ExpectDeprecationTrait;
diff --git a/core/tests/Drupal/Tests/Core/Test/TestSuiteBaseTest.php b/core/tests/Drupal/Tests/Core/Test/TestSuiteBaseTest.php
index f9e8142318..946a47b162 100644
--- a/core/tests/Drupal/Tests/Core/Test/TestSuiteBaseTest.php
+++ b/core/tests/Drupal/Tests/Core/Test/TestSuiteBaseTest.php
@@ -2,7 +2,7 @@
 
 namespace Drupal\Tests\Core\Test;
 
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 use Drupal\Tests\TestSuites\TestSuiteBase;
 use org\bovigo\vfs\vfsStream;
 use PHPUnit\Framework\TestCase;
@@ -15,7 +15,7 @@
 // dynamically load a compatibility trait dependent on the PHPUnit runner
 // version.
 if (!trait_exists(PhpunitVersionDependentStubTestSuiteBaseTrait::class, FALSE)) {
-  class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\StubTestSuiteBaseTrait", PhpunitVersionDependentStubTestSuiteBaseTrait::class);
+  class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\StubTestSuiteBaseTrait", PhpunitVersionDependentStubTestSuiteBaseTrait::class);
 }
 
 /**
diff --git a/core/tests/Drupal/Tests/Listeners/AfterSymfonyListener.php b/core/tests/Drupal/Tests/Listeners/AfterSymfonyListener.php
index 7123dfac65..a6ad26baf3 100644
--- a/core/tests/Drupal/Tests/Listeners/AfterSymfonyListener.php
+++ b/core/tests/Drupal/Tests/Listeners/AfterSymfonyListener.php
@@ -10,6 +10,6 @@
 
 namespace Drupal\Tests\Listeners;
 
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 
-class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\AfterSymfonyListener", AfterSymfonyListener::class);
+class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\AfterSymfonyListener", AfterSymfonyListener::class);
diff --git a/core/tests/Drupal/Tests/Listeners/DrupalListener.php b/core/tests/Drupal/Tests/Listeners/DrupalListener.php
index 5dc803f526..5fd3d34742 100644
--- a/core/tests/Drupal/Tests/Listeners/DrupalListener.php
+++ b/core/tests/Drupal/Tests/Listeners/DrupalListener.php
@@ -10,6 +10,6 @@
 
 namespace Drupal\Tests\Listeners;
 
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 
-class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\DrupalListener", DrupalListener::class);
+class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\DrupalListener", DrupalListener::class);
diff --git a/core/tests/Drupal/Tests/Listeners/HtmlOutputPrinter.php b/core/tests/Drupal/Tests/Listeners/HtmlOutputPrinter.php
index 2227d31c28..c53ad8eb3b 100644
--- a/core/tests/Drupal/Tests/Listeners/HtmlOutputPrinter.php
+++ b/core/tests/Drupal/Tests/Listeners/HtmlOutputPrinter.php
@@ -10,6 +10,6 @@
 
 namespace Drupal\Tests\Listeners;
 
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 
-class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\HtmlOutputPrinter", HtmlOutputPrinter::class);
+class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\HtmlOutputPrinter", HtmlOutputPrinter::class);
diff --git a/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php b/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php
index 87f8f9ff95..c34edca957 100644
--- a/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php
+++ b/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php
@@ -10,6 +10,6 @@
 
 namespace Drupal\Tests\Listeners;
 
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 
-class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\SimpletestUiPrinter", SimpletestUiPrinter::class);
+class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\SimpletestUiPrinter", SimpletestUiPrinter::class);
diff --git a/core/tests/Drupal/Tests/PhpunitCompatibilityTrait.php b/core/tests/Drupal/Tests/PhpunitCompatibilityTrait.php
index 043bc0fbdd..8f604bc68b 100644
--- a/core/tests/Drupal/Tests/PhpunitCompatibilityTrait.php
+++ b/core/tests/Drupal/Tests/PhpunitCompatibilityTrait.php
@@ -2,13 +2,13 @@
 
 namespace Drupal\Tests;
 
-use Drupal\Core\Test\PhpUnitCompatibility\RunnerVersion;
+use Drupal\Tool\PhpUnit\PhpUnitCompatibility\RunnerVersion;
 
 // In order to manage different method signatures between PHPUnit versions, we
 // dynamically load a compatibility trait dependent on the PHPUnit runner
 // version.
 if (!trait_exists(PhpunitVersionDependentTestCompatibilityTrait::class, FALSE)) {
-  class_alias("Drupal\Core\Test\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\TestCompatibilityTrait", PhpunitVersionDependentTestCompatibilityTrait::class);
+  class_alias("Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit" . RunnerVersion::getMajor() . "\TestCompatibilityTrait", PhpunitVersionDependentTestCompatibilityTrait::class);
 }
 
 /**
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/AfterSymfonyListener.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/AfterSymfonyListener.php
similarity index 86%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/AfterSymfonyListener.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/AfterSymfonyListener.php
index 7fee8fc67d..a1c0ec4bf0 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/AfterSymfonyListener.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/AfterSymfonyListener.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 use PHPUnit\Framework\Test;
 use PHPUnit\Framework\TestListener;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/DrupalListener.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/DrupalListener.php
similarity index 93%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/DrupalListener.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/DrupalListener.php
index 15a6db56c0..c2dad8b61d 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/DrupalListener.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/DrupalListener.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 use Drupal\Tests\Listeners\DeprecationListenerTrait;
 use Drupal\Tests\Listeners\DrupalComponentTestListenerTrait;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/FileFieldTestBaseTrait.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/FileFieldTestBaseTrait.php
similarity index 97%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/FileFieldTestBaseTrait.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/FileFieldTestBaseTrait.php
index 753c0392be..f832edcaba 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/FileFieldTestBaseTrait.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/FileFieldTestBaseTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\file\FileInterface;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/HtmlOutputPrinter.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/HtmlOutputPrinter.php
similarity index 88%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/HtmlOutputPrinter.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/HtmlOutputPrinter.php
index 2e92a9dba0..3008313161 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/HtmlOutputPrinter.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/HtmlOutputPrinter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 use Drupal\Tests\Listeners\HtmlOutputPrinterTrait;
 use PHPUnit\Framework\TestResult;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/SimpletestUiPrinter.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/SimpletestUiPrinter.php
similarity index 80%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/SimpletestUiPrinter.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/SimpletestUiPrinter.php
index ede759f075..c15ee3af2e 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/SimpletestUiPrinter.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/SimpletestUiPrinter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 /**
  * Defines a class for providing html output links in the Simpletest UI.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/StubTestSuiteBaseTrait.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/StubTestSuiteBaseTrait.php
similarity index 90%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/StubTestSuiteBaseTrait.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/StubTestSuiteBaseTrait.php
index 4b38eb710c..b758307424 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/StubTestSuiteBaseTrait.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/StubTestSuiteBaseTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 /**
  * Makes Drupal's test API forward compatible with multiple versions of PHPUnit.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/TestCompatibilityTrait.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/TestCompatibilityTrait.php
similarity index 96%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/TestCompatibilityTrait.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/TestCompatibilityTrait.php
index c7623ac1ab..d36d06a597 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit6/TestCompatibilityTrait.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit6/TestCompatibilityTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit6;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit6;
 
 /**
  * Makes Drupal's test API forward compatible with multiple versions of PHPUnit.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/AfterSymfonyListener.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/AfterSymfonyListener.php
similarity index 86%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/AfterSymfonyListener.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/AfterSymfonyListener.php
index bdb1fd4603..7353b705c2 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/AfterSymfonyListener.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/AfterSymfonyListener.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 use PHPUnit\Framework\Test;
 use PHPUnit\Framework\TestListener;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/DrupalListener.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/DrupalListener.php
similarity index 93%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/DrupalListener.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/DrupalListener.php
index 92e35cd241..41ad00c443 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/DrupalListener.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/DrupalListener.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 use Drupal\Tests\Listeners\DeprecationListenerTrait;
 use Drupal\Tests\Listeners\DrupalComponentTestListenerTrait;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/FileFieldTestBaseTrait.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/FileFieldTestBaseTrait.php
similarity index 72%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/FileFieldTestBaseTrait.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/FileFieldTestBaseTrait.php
index 64bc02bf3a..a36bbb80b1 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/FileFieldTestBaseTrait.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/FileFieldTestBaseTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 /**
  * Makes Drupal's test API forward compatible with multiple versions of PHPUnit.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/HtmlOutputPrinter.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/HtmlOutputPrinter.php
similarity index 88%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/HtmlOutputPrinter.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/HtmlOutputPrinter.php
index da6592d69e..d481feeaff 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/HtmlOutputPrinter.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/HtmlOutputPrinter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 use Drupal\Tests\Listeners\HtmlOutputPrinterTrait;
 use PHPUnit\Framework\TestResult;
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/SimpletestUiPrinter.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/SimpletestUiPrinter.php
similarity index 81%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/SimpletestUiPrinter.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/SimpletestUiPrinter.php
index ac9fca6b9c..3759bd6394 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/SimpletestUiPrinter.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/SimpletestUiPrinter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 /**
  * Defines a class for providing html output links in the Simpletest UI.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/StubTestSuiteBaseTrait.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/StubTestSuiteBaseTrait.php
similarity index 90%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/StubTestSuiteBaseTrait.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/StubTestSuiteBaseTrait.php
index 247028f545..b41e57c20c 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/StubTestSuiteBaseTrait.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/StubTestSuiteBaseTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 /**
  * Makes Drupal's test API forward compatible with multiple versions of PHPUnit.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/TestCompatibilityTrait.php b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/TestCompatibilityTrait.php
similarity index 96%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/TestCompatibilityTrait.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/TestCompatibilityTrait.php
index b5f021f343..7f8300b57a 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/PhpUnit7/TestCompatibilityTrait.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/PhpUnit7/TestCompatibilityTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility\PhpUnit7;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility\PhpUnit7;
 
 /**
  * Makes Drupal's test API forward compatible with multiple versions of PHPUnit.
diff --git a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/RunnerVersion.php b/core/tools/PhpUnit/PhpUnitCompatibility/RunnerVersion.php
similarity index 91%
rename from core/lib/Drupal/Core/Test/PhpUnitCompatibility/RunnerVersion.php
rename to core/tools/PhpUnit/PhpUnitCompatibility/RunnerVersion.php
index f6282456f5..50b69dc2ab 100644
--- a/core/lib/Drupal/Core/Test/PhpUnitCompatibility/RunnerVersion.php
+++ b/core/tools/PhpUnit/PhpUnitCompatibility/RunnerVersion.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\Core\Test\PhpUnitCompatibility;
+namespace Drupal\Tool\PhpUnit\PhpUnitCompatibility;
 
 use PHPUnit\Runner\Version;