diff --git a/core/modules/basic_auth/tests/src/Traits/BasicAuthTestTrait.php b/core/modules/basic_auth/tests/src/Traits/BasicAuthTestTrait.php
index 15de6407d5b389c30181827874ddac07eeecb65d..c7494b46137fdc29d16206e3a2051c0b0024d115 100644
--- a/core/modules/basic_auth/tests/src/Traits/BasicAuthTestTrait.php
+++ b/core/modules/basic_auth/tests/src/Traits/BasicAuthTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\basic_auth\Traits;
 
 /**
diff --git a/core/modules/block/tests/src/Traits/BlockCreationTrait.php b/core/modules/block/tests/src/Traits/BlockCreationTrait.php
index 440f34c10da8069afe2146fbcb4b398fc2b97feb..e94767409893dd24a223f9c1092996b74b400c12 100644
--- a/core/modules/block/tests/src/Traits/BlockCreationTrait.php
+++ b/core/modules/block/tests/src/Traits/BlockCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\block\Traits;
 
 use Drupal\block\Entity\Block;
diff --git a/core/modules/ckeditor5/tests/src/Traits/CKEditor5TestTrait.php b/core/modules/ckeditor5/tests/src/Traits/CKEditor5TestTrait.php
index 1556312b6824eb4bb2dd49fc56a072509b4df057..ab08838ccfe00172da8312cd0ae40b6686b1e146 100644
--- a/core/modules/ckeditor5/tests/src/Traits/CKEditor5TestTrait.php
+++ b/core/modules/ckeditor5/tests/src/Traits/CKEditor5TestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\ckeditor5\Traits;
 
 use Behat\Mink\Element\NodeElement;
diff --git a/core/modules/ckeditor5/tests/src/Traits/PrivateMethodUnitTestTrait.php b/core/modules/ckeditor5/tests/src/Traits/PrivateMethodUnitTestTrait.php
index 9a2a2c7210f832b00f0b7f408c0032a02ea6d291..5a28ea8b7581f7d9f3e469d85f69626a5682e866 100644
--- a/core/modules/ckeditor5/tests/src/Traits/PrivateMethodUnitTestTrait.php
+++ b/core/modules/ckeditor5/tests/src/Traits/PrivateMethodUnitTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\ckeditor5\Traits;
 
 /**
diff --git a/core/modules/ckeditor5/tests/src/Traits/SynchronizeCsrfTokenSeedTrait.php b/core/modules/ckeditor5/tests/src/Traits/SynchronizeCsrfTokenSeedTrait.php
index 11d5d1f14b872e1f5fcdfaf3d5de922c45b2ebb5..2ec5308000ddf8b6c07ae527820919be067392ef 100644
--- a/core/modules/ckeditor5/tests/src/Traits/SynchronizeCsrfTokenSeedTrait.php
+++ b/core/modules/ckeditor5/tests/src/Traits/SynchronizeCsrfTokenSeedTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\ckeditor5\Traits;
 
 use Drupal\Core\Session\AccountInterface;
diff --git a/core/modules/config/tests/src/Traits/AssertConfigEntityImportTrait.php b/core/modules/config/tests/src/Traits/AssertConfigEntityImportTrait.php
index 7cae45f0240ab2e3daf01599b2a2dd080891cb1e..f6f83454de4d18c5bf8c1603d94719c4bb0d445c 100644
--- a/core/modules/config/tests/src/Traits/AssertConfigEntityImportTrait.php
+++ b/core/modules/config/tests/src/Traits/AssertConfigEntityImportTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\config\Traits;
 
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
diff --git a/core/modules/content_moderation/tests/src/Traits/ContentModerationTestTrait.php b/core/modules/content_moderation/tests/src/Traits/ContentModerationTestTrait.php
index 2b2014373edbebd36fa469bdf0b8414573868fe7..9c5d9ccf5d196bff5c17c7852dec4f9869766841 100644
--- a/core/modules/content_moderation/tests/src/Traits/ContentModerationTestTrait.php
+++ b/core/modules/content_moderation/tests/src/Traits/ContentModerationTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\content_moderation\Traits;
 
 use Drupal\workflows\Entity\Workflow;
diff --git a/core/modules/field/tests/src/Traits/EntityReferenceFieldCreationTrait.php b/core/modules/field/tests/src/Traits/EntityReferenceFieldCreationTrait.php
index 42edf6a3416909e39b91f6091c7e1361805a72c2..d0049fbcfe4456c7239febe68c83f0758e0a93ae 100644
--- a/core/modules/field/tests/src/Traits/EntityReferenceFieldCreationTrait.php
+++ b/core/modules/field/tests/src/Traits/EntityReferenceFieldCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\field\Traits;
 
 use Drupal\field\Entity\FieldConfig;
diff --git a/core/modules/field/tests/src/Traits/EntityReferenceTestTrait.php b/core/modules/field/tests/src/Traits/EntityReferenceTestTrait.php
index 1820a738d8011bcaa9293001b846302b766bde7a..50a8a3126d562ff851c0df9525ad038692e322b2 100644
--- a/core/modules/field/tests/src/Traits/EntityReferenceTestTrait.php
+++ b/core/modules/field/tests/src/Traits/EntityReferenceTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\field\Traits;
 
 @trigger_error('The ' . __NAMESPACE__ . '\EntityReferenceTestTrait is deprecated in drupal:10.2.0 and is removed from drupal:11.0.0. Instead, use \Drupal\Tests\field\Traits\EntityReferenceFieldCreationTrait. See https://www.drupal.org/node/3401941', E_USER_DEPRECATED);
diff --git a/core/modules/field_ui/tests/src/Traits/FieldUiJSTestTrait.php b/core/modules/field_ui/tests/src/Traits/FieldUiJSTestTrait.php
index 2630b36815b76c3876f328781542852b4a38f47e..cba90a5bb4bb5cfa0f6f427076351bdeba4541e8 100644
--- a/core/modules/field_ui/tests/src/Traits/FieldUiJSTestTrait.php
+++ b/core/modules/field_ui/tests/src/Traits/FieldUiJSTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\field_ui\Traits;
 
 /**
diff --git a/core/modules/field_ui/tests/src/Traits/FieldUiTestTrait.php b/core/modules/field_ui/tests/src/Traits/FieldUiTestTrait.php
index a381c4ac68581a34bfa5ae8885a0fa68d3bf99b8..87e835f7ceadd62f9aa1b2528dfc56208ce8a904 100644
--- a/core/modules/field_ui/tests/src/Traits/FieldUiTestTrait.php
+++ b/core/modules/field_ui/tests/src/Traits/FieldUiTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\field_ui\Traits;
 
 use Behat\Mink\Exception\ElementNotFoundException;
diff --git a/core/modules/jsonapi/tests/src/Traits/CommonCollectionFilterAccessTestPatternsTrait.php b/core/modules/jsonapi/tests/src/Traits/CommonCollectionFilterAccessTestPatternsTrait.php
index 60266a44b95b1922122af9f3f7fd5e08c8e75b02..35f84c346cd7272854d4e75548473d5b169c04d9 100644
--- a/core/modules/jsonapi/tests/src/Traits/CommonCollectionFilterAccessTestPatternsTrait.php
+++ b/core/modules/jsonapi/tests/src/Traits/CommonCollectionFilterAccessTestPatternsTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\jsonapi\Traits;
 
 use Drupal\Component\Serialization\Json;
diff --git a/core/modules/media/tests/src/Traits/MediaTypeCreationTrait.php b/core/modules/media/tests/src/Traits/MediaTypeCreationTrait.php
index 0e87a6ec8e6c202bbd7810969e77e38b8d062d8c..8059c9ca9c5e01feaa1d48fb985c8a71f9887aca 100644
--- a/core/modules/media/tests/src/Traits/MediaTypeCreationTrait.php
+++ b/core/modules/media/tests/src/Traits/MediaTypeCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\media\Traits;
 
 use Drupal\media\Entity\MediaType;
diff --git a/core/modules/media/tests/src/Traits/OEmbedTestTrait.php b/core/modules/media/tests/src/Traits/OEmbedTestTrait.php
index 8744bffef12d2720d1809967c50a2aaf7bf392b3..0219be2007fcdcbd196dfe62436442ebe60af650 100644
--- a/core/modules/media/tests/src/Traits/OEmbedTestTrait.php
+++ b/core/modules/media/tests/src/Traits/OEmbedTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\media\Traits;
 
 use Drupal\Component\Serialization\Json;
diff --git a/core/modules/menu_ui/tests/src/Traits/MenuUiTrait.php b/core/modules/menu_ui/tests/src/Traits/MenuUiTrait.php
index d9eaa78c67f9b566783e68de6b4e34d968dfbd06..6c41d7bf79fdc8390a2cc85f3e068204e166b1ef 100644
--- a/core/modules/menu_ui/tests/src/Traits/MenuUiTrait.php
+++ b/core/modules/menu_ui/tests/src/Traits/MenuUiTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\menu_ui\Traits;
 
 /**
diff --git a/core/modules/migrate_drupal/tests/src/Traits/CreateMigrationsTrait.php b/core/modules/migrate_drupal/tests/src/Traits/CreateMigrationsTrait.php
index 9b316de2ae8789b9c7e6edc4e1b15335dbe1ac28..25a6ea4237d61bfc0299d7bf70230cf4ccb146f4 100644
--- a/core/modules/migrate_drupal/tests/src/Traits/CreateMigrationsTrait.php
+++ b/core/modules/migrate_drupal/tests/src/Traits/CreateMigrationsTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\migrate_drupal\Traits;
 
 trait CreateMigrationsTrait {
diff --git a/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php b/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php
index 05da0215f9ecf943bf1119820356352f13cf3da1..1f792f450e7f4fc33dd6b75720a10b1e5b0f1ff3 100644
--- a/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php
+++ b/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\migrate_drupal\Traits;
 
 /**
diff --git a/core/modules/migrate_drupal/tests/src/Traits/FieldDiscoveryTestTrait.php b/core/modules/migrate_drupal/tests/src/Traits/FieldDiscoveryTestTrait.php
index 34a16ad85ea75310db69473dc949c3b399b71bce..b51fe785ae43d49c6a942453cf5941d0c1436f03 100644
--- a/core/modules/migrate_drupal/tests/src/Traits/FieldDiscoveryTestTrait.php
+++ b/core/modules/migrate_drupal/tests/src/Traits/FieldDiscoveryTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\migrate_drupal\Traits;
 
 use Drupal\field_discovery_test\FieldDiscoveryTestClass;
diff --git a/core/modules/migrate_drupal/tests/src/Traits/NodeMigrateTypeTestTrait.php b/core/modules/migrate_drupal/tests/src/Traits/NodeMigrateTypeTestTrait.php
index 19b59068ba01d2d851f96399698624b3b7db9d85..b8939fda87b51db88536611fd0aa415bc055e8bb 100644
--- a/core/modules/migrate_drupal/tests/src/Traits/NodeMigrateTypeTestTrait.php
+++ b/core/modules/migrate_drupal/tests/src/Traits/NodeMigrateTypeTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\migrate_drupal\Traits;
 
 use Drupal\migrate_drupal\NodeMigrateType;
diff --git a/core/modules/migrate_drupal/tests/src/Traits/ValidateMigrationStateTestTrait.php b/core/modules/migrate_drupal/tests/src/Traits/ValidateMigrationStateTestTrait.php
index 61ab00d862328d96bb8f911ceee2f1fbe74df4c0..a7378e5a7e723bfb62a98866a4dbeea38abd36c8 100644
--- a/core/modules/migrate_drupal/tests/src/Traits/ValidateMigrationStateTestTrait.php
+++ b/core/modules/migrate_drupal/tests/src/Traits/ValidateMigrationStateTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\migrate_drupal\Traits;
 
 use Drupal\Component\Discovery\YamlDiscovery;
diff --git a/core/modules/node/tests/src/Traits/ContentTypeCreationTrait.php b/core/modules/node/tests/src/Traits/ContentTypeCreationTrait.php
index 127207894e81acb4ef1f00f1d9222dba83f891eb..5f87bcc35bcdd95aeb1daadc8ee658e71c83e4f3 100644
--- a/core/modules/node/tests/src/Traits/ContentTypeCreationTrait.php
+++ b/core/modules/node/tests/src/Traits/ContentTypeCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\node\Traits;
 
 use Drupal\Component\Render\FormattableMarkup;
diff --git a/core/modules/node/tests/src/Traits/NodeCreationTrait.php b/core/modules/node/tests/src/Traits/NodeCreationTrait.php
index 7ec87f54c92b87dfd70329db28465ce4d27f51a9..8f811064421fa4e5262ce05acc75666da85d9424 100644
--- a/core/modules/node/tests/src/Traits/NodeCreationTrait.php
+++ b/core/modules/node/tests/src/Traits/NodeCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\node\Traits;
 
 use Drupal\node\Entity\Node;
diff --git a/core/modules/system/tests/src/Traits/OffCanvasTestTrait.php b/core/modules/system/tests/src/Traits/OffCanvasTestTrait.php
index a406c6f44ae5d92dcf09f811662a34ba695a7837..428ffdf7990c013645a118e66f2541ef53007d5c 100644
--- a/core/modules/system/tests/src/Traits/OffCanvasTestTrait.php
+++ b/core/modules/system/tests/src/Traits/OffCanvasTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\system\Traits;
 
 /**
diff --git a/core/modules/system/tests/src/Traits/TestTrait.php b/core/modules/system/tests/src/Traits/TestTrait.php
index 02ef094bc1d2264022653909d3869071505282f1..c35f499c6c67c66ead05f7847903490fbc7e6148 100644
--- a/core/modules/system/tests/src/Traits/TestTrait.php
+++ b/core/modules/system/tests/src/Traits/TestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\system\Traits;
 
 /**
diff --git a/core/modules/taxonomy/tests/src/Traits/TaxonomyTestTrait.php b/core/modules/taxonomy/tests/src/Traits/TaxonomyTestTrait.php
index 4df0f1a293358cecfb4f542a8a0074f3ad1dffaf..e0a858b367265a4b2508f5880e916f602560f6c1 100644
--- a/core/modules/taxonomy/tests/src/Traits/TaxonomyTestTrait.php
+++ b/core/modules/taxonomy/tests/src/Traits/TaxonomyTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\taxonomy\Traits;
 
 use Drupal\Core\Language\LanguageInterface;
diff --git a/core/modules/user/tests/src/Traits/UserCreationTrait.php b/core/modules/user/tests/src/Traits/UserCreationTrait.php
index d51bc4bd1170c2496a87aa7936f8b9dc0c13f221..510d722ebd55a496d9c1dee9882a81b32d36acdd 100644
--- a/core/modules/user/tests/src/Traits/UserCreationTrait.php
+++ b/core/modules/user/tests/src/Traits/UserCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\user\Traits;
 
 use Drupal\Core\Database\DatabaseExceptionWrapper;
diff --git a/core/modules/views/tests/src/Traits/ViewsLoggerTestTrait.php b/core/modules/views/tests/src/Traits/ViewsLoggerTestTrait.php
index bea149498d45d0f146f65a80af2dcf6095d00470..734e702f418bf0a92c8f7bdb1fa65c8d1e066fcc 100644
--- a/core/modules/views/tests/src/Traits/ViewsLoggerTestTrait.php
+++ b/core/modules/views/tests/src/Traits/ViewsLoggerTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\views\Traits;
 
 use Drupal\Core\Logger\LoggerChannelFactoryInterface;
diff --git a/core/phpcs.xml.dist b/core/phpcs.xml.dist
index 015d8633e3bb59942f881dd76e1d26506f7afc48..74776964a318094c235349d86a090fe1e6873bf2 100644
--- a/core/phpcs.xml.dist
+++ b/core/phpcs.xml.dist
@@ -272,7 +272,13 @@
     <properties>
       <property name="spacesCountAroundEqualsSign" value="0" />
     </properties>
+    <!-- @todo Broaden this in https://www.drupal.org/project/drupal/issues/3400434 -->
+    <!-- <include-pattern>*/tests/*</include-pattern> -->
     <include-pattern>./tests/Drupal/BuildTests/*</include-pattern>
+    <include-pattern>*/tests/src/Traits/*</include-pattern>
+    <include-pattern>./tests/Drupal/Tests/*Trait.php</include-pattern>
+    <include-pattern>./tests/Drupal/Tests/Traits/*</include-pattern>
+    <exclude-pattern>./tests/Drupal/Tests/Listeners/*</exclude-pattern>
   </rule>
 
   <!-- Squiz sniffs -->
diff --git a/core/tests/Drupal/Tests/ApiRequestTrait.php b/core/tests/Drupal/Tests/ApiRequestTrait.php
index 83888277415bd51312514a4be16fd6ba9ece5285..12db34c52b55da54874ff4d9e2369312d28b5667 100644
--- a/core/tests/Drupal/Tests/ApiRequestTrait.php
+++ b/core/tests/Drupal/Tests/ApiRequestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Behat\Mink\Driver\BrowserKitDriver;
diff --git a/core/tests/Drupal/Tests/BrowserHtmlDebugTrait.php b/core/tests/Drupal/Tests/BrowserHtmlDebugTrait.php
index 64c9566a6529ded71efc4c1556c2ec1335b3d1f5..0ce61082fd1809114316a1e5906b832a6d6c0d59 100644
--- a/core/tests/Drupal/Tests/BrowserHtmlDebugTrait.php
+++ b/core/tests/Drupal/Tests/BrowserHtmlDebugTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Component\Utility\Html;
diff --git a/core/tests/Drupal/Tests/Composer/ComposerIntegrationTrait.php b/core/tests/Drupal/Tests/Composer/ComposerIntegrationTrait.php
index 9cebb60551d2f766e35ec33d02648606f1780dd3..595e4bef877f17214e920f6593dd97c53ca16bd1 100644
--- a/core/tests/Drupal/Tests/Composer/ComposerIntegrationTrait.php
+++ b/core/tests/Drupal/Tests/Composer/ComposerIntegrationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Composer;
 
 use Symfony\Component\Finder\Finder;
diff --git a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/AssertUtilsTrait.php b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/AssertUtilsTrait.php
index ecbd4f83c123b39af595532b1e2f232163f0b9ed..a2257158b2c595a543a2a72788c0569c23075c03 100644
--- a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/AssertUtilsTrait.php
+++ b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/AssertUtilsTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Composer\Plugin\Scaffold;
 
 use Drupal\Tests\Traits\PhpUnitWarnings;
diff --git a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/ExecTrait.php b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/ExecTrait.php
index be29f84561ca49a879884721d8df896407e4fcb9..976005a31ffce104ae793160f350243311f280c3 100644
--- a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/ExecTrait.php
+++ b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/ExecTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Composer\Plugin\Scaffold;
 
 use Symfony\Component\Process\Process;
diff --git a/core/tests/Drupal/Tests/ConfigTestTrait.php b/core/tests/Drupal/Tests/ConfigTestTrait.php
index 7ecc541772a6df75f2b99fa748d05e1388ad67a0..31d010dd9427e660cdc9a1950b386bf480c40d10 100644
--- a/core/tests/Drupal/Tests/ConfigTestTrait.php
+++ b/core/tests/Drupal/Tests/ConfigTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\Config\ConfigImporter;
diff --git a/core/tests/Drupal/Tests/Core/Database/SchemaIntrospectionTestTrait.php b/core/tests/Drupal/Tests/Core/Database/SchemaIntrospectionTestTrait.php
index 5e89de4ca572bc84b14af95a6fa0de75dc59cdcd..b9e4068c278961f530208b29b929edb84c38f5b5 100644
--- a/core/tests/Drupal/Tests/Core/Database/SchemaIntrospectionTestTrait.php
+++ b/core/tests/Drupal/Tests/Core/Database/SchemaIntrospectionTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Core\Database;
 
 /**
diff --git a/core/tests/Drupal/Tests/EntityViewTrait.php b/core/tests/Drupal/Tests/EntityViewTrait.php
index 6f7fad2946757c28e149b2b481882f15f9a651a2..a1568119f8b61b9f71d143c7761fd5a42a16994f 100644
--- a/core/tests/Drupal/Tests/EntityViewTrait.php
+++ b/core/tests/Drupal/Tests/EntityViewTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\Entity\EntityInterface;
diff --git a/core/tests/Drupal/Tests/ExtensionListTestTrait.php b/core/tests/Drupal/Tests/ExtensionListTestTrait.php
index 088237893bb70aeb567c751f2719b7caf74a063a..04f88bf2610e3de935316973e4c998eaaf0476f2 100644
--- a/core/tests/Drupal/Tests/ExtensionListTestTrait.php
+++ b/core/tests/Drupal/Tests/ExtensionListTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 /**
diff --git a/core/tests/Drupal/Tests/PerformanceTestTrait.php b/core/tests/Drupal/Tests/PerformanceTestTrait.php
index 9f910d338775245d51918c4ce060868938de5fa1..332ae4540953d60ed68617024d67c256dd5d4d5d 100644
--- a/core/tests/Drupal/Tests/PerformanceTestTrait.php
+++ b/core/tests/Drupal/Tests/PerformanceTestTrait.php
@@ -1,6 +1,6 @@
 <?php
 
-declare(strict_types = 1);
+declare(strict_types=1);
 
 namespace Drupal\Tests;
 
diff --git a/core/tests/Drupal/Tests/PhpUnitCompatibilityTrait.php b/core/tests/Drupal/Tests/PhpUnitCompatibilityTrait.php
index 1192c2e246cc653e293b642c7718d26e4c3be9d3..3bba95e3a761c0f27f5bedb4136c51c9af4cac70 100644
--- a/core/tests/Drupal/Tests/PhpUnitCompatibilityTrait.php
+++ b/core/tests/Drupal/Tests/PhpUnitCompatibilityTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\TestTools\PhpUnitCompatibility\RunnerVersion;
diff --git a/core/tests/Drupal/Tests/RandomGeneratorTrait.php b/core/tests/Drupal/Tests/RandomGeneratorTrait.php
index eccac674f1b414f42e79d3a2ea01c8f031c3d7a7..380b38d7384927c6def4fdf50bcc845a53503e21 100644
--- a/core/tests/Drupal/Tests/RandomGeneratorTrait.php
+++ b/core/tests/Drupal/Tests/RandomGeneratorTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\TestTools\Random;
diff --git a/core/tests/Drupal/Tests/RequirementsPageTrait.php b/core/tests/Drupal/Tests/RequirementsPageTrait.php
index 6bc47909c77d614c7c5ed38b3f84a89ee33a3f3b..c10e5676079d124648447ec4d0296118bf166ea9 100644
--- a/core/tests/Drupal/Tests/RequirementsPageTrait.php
+++ b/core/tests/Drupal/Tests/RequirementsPageTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\Utility\PhpRequirements;
diff --git a/core/tests/Drupal/Tests/SchemaCheckTestTrait.php b/core/tests/Drupal/Tests/SchemaCheckTestTrait.php
index 73f8dc5c8c6cbcecbf9955bdcd2d29302d7a08e1..26f97c482b4c45b25eb6a7ab78afcba379a005d2 100644
--- a/core/tests/Drupal/Tests/SchemaCheckTestTrait.php
+++ b/core/tests/Drupal/Tests/SchemaCheckTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\Config\TypedConfigManagerInterface;
diff --git a/core/tests/Drupal/Tests/SessionTestTrait.php b/core/tests/Drupal/Tests/SessionTestTrait.php
index e71fdf256bdbb3932fa1ea345505e37b5eb4c5a9..d06f6af7a78ccbd91224b8ab68d8e1f5ed6673aa 100644
--- a/core/tests/Drupal/Tests/SessionTestTrait.php
+++ b/core/tests/Drupal/Tests/SessionTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Symfony\Component\HttpFoundation\Request;
diff --git a/core/tests/Drupal/Tests/TestFileCreationTrait.php b/core/tests/Drupal/Tests/TestFileCreationTrait.php
index 5f401975dce0b65d5101830a1f9d22e54ee7420a..f7445584add3a41d426ffdc20e675a22a4110aaf 100644
--- a/core/tests/Drupal/Tests/TestFileCreationTrait.php
+++ b/core/tests/Drupal/Tests/TestFileCreationTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\StreamWrapper\PublicStream;
diff --git a/core/tests/Drupal/Tests/TestRequirementsTrait.php b/core/tests/Drupal/Tests/TestRequirementsTrait.php
index e7a9548fee39b3a489b060b10beedbd87a49c5c7..8dae05cf3789bcba6fea8fae15b2298d4d359447 100644
--- a/core/tests/Drupal/Tests/TestRequirementsTrait.php
+++ b/core/tests/Drupal/Tests/TestRequirementsTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\Extension\ExtensionDiscovery;
diff --git a/core/tests/Drupal/Tests/Traits/Core/Config/SchemaConfigListenerTestTrait.php b/core/tests/Drupal/Tests/Traits/Core/Config/SchemaConfigListenerTestTrait.php
index 62552d4dc2d1fd63744e5a42e04aa9c5226810de..89493d5ef4aad7a341661901d3e7ee10bed30032 100644
--- a/core/tests/Drupal/Tests/Traits/Core/Config/SchemaConfigListenerTestTrait.php
+++ b/core/tests/Drupal/Tests/Traits/Core/Config/SchemaConfigListenerTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Traits\Core\Config;
 
 use Drupal\Core\Config\Schema\SchemaIncompleteException;
diff --git a/core/tests/Drupal/Tests/Traits/Core/CronRunTrait.php b/core/tests/Drupal/Tests/Traits/Core/CronRunTrait.php
index 17ca9fcdb6f132a91b5c73d111db5124974caf71..02f271edebc8ec2ba0bca1c3f749af4f07d540b5 100644
--- a/core/tests/Drupal/Tests/Traits/Core/CronRunTrait.php
+++ b/core/tests/Drupal/Tests/Traits/Core/CronRunTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Traits\Core;
 
 /**
diff --git a/core/tests/Drupal/Tests/Traits/Core/GeneratePermutationsTrait.php b/core/tests/Drupal/Tests/Traits/Core/GeneratePermutationsTrait.php
index 6e222cb65632ee04079f5fc72fb432d5d5375b13..6bd903633a0fe2ae6269d822422565d1316bfef1 100644
--- a/core/tests/Drupal/Tests/Traits/Core/GeneratePermutationsTrait.php
+++ b/core/tests/Drupal/Tests/Traits/Core/GeneratePermutationsTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Traits\Core;
 
 /**
diff --git a/core/tests/Drupal/Tests/Traits/Core/Image/ToolkitTestTrait.php b/core/tests/Drupal/Tests/Traits/Core/Image/ToolkitTestTrait.php
index 45f9ca7816325959e6b5a4df94fb80bd09c75ac0..d7b03ccba683213740ca9ab528a8eb630c9a41af 100644
--- a/core/tests/Drupal/Tests/Traits/Core/Image/ToolkitTestTrait.php
+++ b/core/tests/Drupal/Tests/Traits/Core/Image/ToolkitTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Traits\Core\Image;
 
 use Drupal\Core\Image\ImageInterface;
diff --git a/core/tests/Drupal/Tests/Traits/Core/PathAliasTestTrait.php b/core/tests/Drupal/Tests/Traits/Core/PathAliasTestTrait.php
index 2167d43716ad7e4e3350d06b35df16e98c70a57e..6d1cfb163a85fbb8552bd7677a5cb9a49c07382a 100644
--- a/core/tests/Drupal/Tests/Traits/Core/PathAliasTestTrait.php
+++ b/core/tests/Drupal/Tests/Traits/Core/PathAliasTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Traits\Core;
 
 use Drupal\Core\Language\LanguageInterface;
diff --git a/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php b/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php
index ba78874c4efa532ea91f556c5a733beb4556333a..180179a8a67a615bb13edc3df34ffdb6be71f0c5 100644
--- a/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php
+++ b/core/tests/Drupal/Tests/Traits/PhpUnitWarnings.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests\Traits;
 
 /**
diff --git a/core/tests/Drupal/Tests/UiHelperTrait.php b/core/tests/Drupal/Tests/UiHelperTrait.php
index e811de7edef67ef2ea454f793be7dfbe2d194078..449cf2a78ecbbf39334df77102fc03a4ed27ab50 100644
--- a/core/tests/Drupal/Tests/UiHelperTrait.php
+++ b/core/tests/Drupal/Tests/UiHelperTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Behat\Mink\Driver\BrowserKitDriver;
diff --git a/core/tests/Drupal/Tests/UpdatePathTestTrait.php b/core/tests/Drupal/Tests/UpdatePathTestTrait.php
index 0abf1cc477d1b27a64e961b7d8d7cdb47df4beaf..ccd930eaa8fbbc3fddf3e6c7dcc1c6b1be091980 100644
--- a/core/tests/Drupal/Tests/UpdatePathTestTrait.php
+++ b/core/tests/Drupal/Tests/UpdatePathTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Drupal\Core\Database\Database;
diff --git a/core/tests/Drupal/Tests/WaitTerminateTestTrait.php b/core/tests/Drupal/Tests/WaitTerminateTestTrait.php
index 008b1555012801054f9055554a993a345d4e3ea6..2423af83f9dd9d65f3c0e4828269da5f37a06c36 100644
--- a/core/tests/Drupal/Tests/WaitTerminateTestTrait.php
+++ b/core/tests/Drupal/Tests/WaitTerminateTestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 /**
diff --git a/core/tests/Drupal/Tests/XdebugRequestTrait.php b/core/tests/Drupal/Tests/XdebugRequestTrait.php
index cfcf4702cd85ec3db500e0c1dc9d62bcfdef6a10..555140b947c1b41b9d579daba51680cca42b88b3 100644
--- a/core/tests/Drupal/Tests/XdebugRequestTrait.php
+++ b/core/tests/Drupal/Tests/XdebugRequestTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Drupal\Tests;
 
 use Symfony\Component\HttpFoundation\Request;