diff --git a/core/modules/ckeditor5/tests/src/FunctionalJavascript/MediaTestBase.php b/core/modules/ckeditor5/tests/src/FunctionalJavascript/MediaTestBase.php
index 3384ec7fa483a06b2b41e0209a1775c72327963d..1ae146a70e593831a0b887f5914e6cb89e335c6d 100644
--- a/core/modules/ckeditor5/tests/src/FunctionalJavascript/MediaTestBase.php
+++ b/core/modules/ckeditor5/tests/src/FunctionalJavascript/MediaTestBase.php
@@ -255,7 +255,7 @@ protected function assertSourceAttributeSame(string $attribute, ?string $value):
    * @return int
    *   The size of the bytes transferred.
    */
-  protected function getLastPreviewRequestTransferSize() {
+  protected function getLastPreviewRequestTransferSize(): int {
     $javascript = <<<JS
 (function(){
   return window.performance
diff --git a/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
index ce88a5dbd0ec516209a790235ec6a68e8cf88b3f..f73e022a56d9026106514c88ec0e09097226fb3d 100644
--- a/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
+++ b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
@@ -159,7 +159,7 @@ protected function assertAnnounceLeaveEditMode(): void {
    * @return int
    *   The number of tabbable elements.
    */
-  protected function getTabbableElementsCount() {
+  protected function getTabbableElementsCount(): int {
     // Mark all tabbable elements.
     $this->getSession()->executeScript("jQuery(window.tabbable.tabbable(document.body)).attr('data-marked', '');");
     // Count all marked elements.
diff --git a/core/modules/datetime/tests/src/Kernel/Views/DateTimeHandlerTestBase.php b/core/modules/datetime/tests/src/Kernel/Views/DateTimeHandlerTestBase.php
index 2caaba3091fc4c74d0e9824cbaee8c03d4239ce5..55b97d8c854f8ebed2cc6bea14bbb5efad636e17 100644
--- a/core/modules/datetime/tests/src/Kernel/Views/DateTimeHandlerTestBase.php
+++ b/core/modules/datetime/tests/src/Kernel/Views/DateTimeHandlerTestBase.php
@@ -119,7 +119,7 @@ protected function setSiteTimezone($timezone) {
    * @return int
    *   Unix timestamp.
    */
-  protected function getUTCEquivalentOfUserNowAsTimestamp() {
+  protected function getUTCEquivalentOfUserNowAsTimestamp(): int {
     $user_now = new DateTimePlus('now', new \DateTimeZone(date_default_timezone_get()));
     $utc_equivalent = new DateTimePlus($user_now->format('Y-m-d H:i:s'), new \DateTimeZone(DateTimeItemInterface::STORAGE_TIMEZONE));
 
diff --git a/core/modules/dblog/tests/src/Kernel/DbLogTest.php b/core/modules/dblog/tests/src/Kernel/DbLogTest.php
index 9bdc36cb98a9aa6363492f06fda3043778a96a53..6ff79f7aff465e4184ac78dd09e8629bca3556d1 100644
--- a/core/modules/dblog/tests/src/Kernel/DbLogTest.php
+++ b/core/modules/dblog/tests/src/Kernel/DbLogTest.php
@@ -83,7 +83,7 @@ public function testInvalidPlaceholders(): void {
    * @return int
    *   Number of new watchdog entries.
    */
-  private function runCron() {
+  private function runCron(): int {
     $connection = Database::getConnection();
     // Get last ID to compare against; log entries get deleted, so we can't
     // reliably add the number of newly created log entries to the current count
diff --git a/core/modules/file/tests/src/Functional/FileListingTest.php b/core/modules/file/tests/src/Functional/FileListingTest.php
index acb919e1d75b00f15acc780602aec8d1e903ae01..cec109455b087781d3cfda6837d2b88a1cbc8909 100644
--- a/core/modules/file/tests/src/Functional/FileListingTest.php
+++ b/core/modules/file/tests/src/Functional/FileListingTest.php
@@ -62,7 +62,7 @@ protected function setUp(): void {
    * @return int
    *   Total usage count.
    */
-  protected function sumUsages($usage) {
+  protected function sumUsages($usage): int {
     $count = 0;
     foreach ($usage as $module) {
       foreach ($module as $entity_type) {
diff --git a/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
index b99b0b29a69fdb9b29ff577604adf359294f5cf1..2a2aa42d25a564eb34fe5c7fc11f8e0f2c359e4e 100644
--- a/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
@@ -214,7 +214,7 @@ protected function checkConfigurableLanguageWeight($state = 'by default') {
    * @return int
    *   Maximum weight of configurable languages.
    */
-  protected function getHighestConfigurableLanguageWeight() {
+  protected function getHighestConfigurableLanguageWeight(): int {
     $max_weight = 0;
 
     $storage = $this->container->get('entity_type.manager')
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php
index 014bbbf600d8feb8fb52f655f72e890f514238fa..0fd7fb464c3262c48f9b660037b34452a0a95f0f 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php
@@ -315,7 +315,7 @@ protected function assertContextualLinkRetainsMouseup(): void {
    * @return int
    *   The element position.
    */
-  protected function getElementVerticalPosition($css_selector, $position_type) {
+  protected function getElementVerticalPosition($css_selector, $position_type): int {
     $this->assertContains($position_type, ['top', 'bottom'], 'Expected position type.');
     return (int) $this->getSession()->evaluateScript("document.querySelector('$css_selector').getBoundingClientRect().$position_type + window.pageYOffset");
   }
diff --git a/core/modules/migrate_drupal/src/Tests/StubTestTrait.php b/core/modules/migrate_drupal/src/Tests/StubTestTrait.php
index 4eca5aa4c65cc005d8e5322f867081017eaab1bc..e1c1e5c2c2ecba3b30c84f21440145b6fdf264e3 100644
--- a/core/modules/migrate_drupal/src/Tests/StubTestTrait.php
+++ b/core/modules/migrate_drupal/src/Tests/StubTestTrait.php
@@ -33,7 +33,7 @@ protected function performStubTest($entity_type_id) {
    * @return int
    *   ID of the created entity.
    */
-  protected function createEntityStub($entity_type_id) {
+  protected function createEntityStub($entity_type_id): int {
     // Create a dummy migration to pass to the destination plugin.
     $definition = [
       'migration_tags' => ['Stub test'],
diff --git a/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php b/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
index 388680bf0ad48e62bd7f4b8357788fbdb3ce48ba..fa2981eb03f09ee15bbbc1c94e8c074b11edd66e 100644
--- a/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
+++ b/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
@@ -466,7 +466,7 @@ protected function stopServer() {
    * @throws \RuntimeException
    *   Thrown when there are no available ports within the range.
    */
-  protected function findAvailablePort() {
+  protected function findAvailablePort(): int {
     $store = new FlockStore(DrupalFilesystem::getOsTemporaryDirectory());
     $lock_factory = new LockFactory($store);
 
@@ -524,7 +524,7 @@ protected function checkPortIsAvailable($port): bool {
    *
    * @return int
    */
-  protected function getPortNumber() {
+  protected function getPortNumber(): int {
     if (empty($this->hostPort)) {
       $this->hostPort = $this->findAvailablePort();
     }
diff --git a/core/tests/Drupal/KernelTests/Core/Cache/DatabaseBackendTest.php b/core/tests/Drupal/KernelTests/Core/Cache/DatabaseBackendTest.php
index b0fa1e64de7c17ab8d3350edaaf94066f0b54dbe..04aa222706b995dcd085e7cddecba8fb1b3abc09 100644
--- a/core/tests/Drupal/KernelTests/Core/Cache/DatabaseBackendTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Cache/DatabaseBackendTest.php
@@ -112,7 +112,7 @@ public function testGarbageCollection(): void {
    * @return int
    *   The number of rows in the test cache bin database table.
    */
-  protected function getNumRows() {
+  protected function getNumRows(): int {
     $table = 'cache_' . $this->testBin;
     $connection = $this->container->get('database');
     $query = $connection->select($table);
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntityDecoupledTranslationRevisionsTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntityDecoupledTranslationRevisionsTest.php
index 0514af5a46c5b9be6d2563c41c8b3d3279a35214..362280b9e5f8d8a8e0d7a23df97d441a821ec689 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/EntityDecoupledTranslationRevisionsTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityDecoupledTranslationRevisionsTest.php
@@ -288,7 +288,7 @@ public function testUntranslatableFields($sequence, $default_translation_affecte
    * @return int
    *   The latest saved revision id.
    */
-  protected function doTestEditSequence($sequence) {
+  protected function doTestEditSequence($sequence): int {
     $revision_id = NULL;
     foreach ($sequence as $index => $step) {
       $this->stepIndex = $index;
diff --git a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
index 46ac4daf36dfea5e86614f1cd6561f0ce8a69d07..8cf07c7cffd9ab4af94b34cea917c54d037a7ae8 100644
--- a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -452,7 +452,7 @@ protected function assertNoID(string $id, string $html): void {
    * @return int
    *   The number of results that are found.
    */
-  protected function getXPathResultCount($query, $html) {
+  protected function getXPathResultCount($query, $html): int {
     $document = Html::load($html);
     $xpath = new \DOMXPath($document);
 
diff --git a/core/tests/Drupal/Tests/TestFileCreationTrait.php b/core/tests/Drupal/Tests/TestFileCreationTrait.php
index eaf25d07736f8a195027704feaed11217ce3f1ee..ef8437c2f89735757c67be7c52ae08fb2cc267fb 100644
--- a/core/tests/Drupal/Tests/TestFileCreationTrait.php
+++ b/core/tests/Drupal/Tests/TestFileCreationTrait.php
@@ -113,7 +113,7 @@ protected function getTestFiles($type, $size = NULL) {
    *
    * @return int
    */
-  protected function compareFiles($file1, $file2) {
+  protected function compareFiles($file1, $file2): int {
     $compare_size = filesize($file1->uri) - filesize($file2->uri);
     if ($compare_size) {
       // Sort by file size.