diff --git a/core/modules/jsonapi/tests/src/Kernel/Query/FilterTest.php b/core/modules/jsonapi/tests/src/Kernel/Query/FilterTest.php
index 51f1a728af124db15b8a06b67065bb3294d2af0a..66c06900136529866779b89b5080cfc06c553b37 100644
--- a/core/modules/jsonapi/tests/src/Kernel/Query/FilterTest.php
+++ b/core/modules/jsonapi/tests/src/Kernel/Query/FilterTest.php
@@ -67,10 +67,10 @@ public function setUp(): void {
     $this->savePaintings([
       ['colors' => ['red'], 'shapes' => ['triangle'], 'title' => 'FIND'],
       ['colors' => ['orange'], 'shapes' => ['circle'], 'title' => 'FIND'],
-      ['colors' => ['orange'], 'shapes' => ['triangle'], 'title' => 'DONT_FIND'],
+      ['colors' => ['orange'], 'shapes' => ['triangle'], 'title' => 'DO_NOT_FIND'],
       ['colors' => ['yellow'], 'shapes' => ['square'], 'title' => 'FIND'],
-      ['colors' => ['yellow'], 'shapes' => ['triangle'], 'title' => 'DONT_FIND'],
-      ['colors' => ['orange'], 'shapes' => ['square'], 'title' => 'DONT_FIND'],
+      ['colors' => ['yellow'], 'shapes' => ['triangle'], 'title' => 'DO_NOT_FIND'],
+      ['colors' => ['orange'], 'shapes' => ['square'], 'title' => 'DO_NOT_FIND'],
     ]);
 
     $this->nodeStorage = $this->container->get('entity_type.manager')->getStorage('node');
diff --git a/core/modules/migrate/tests/modules/migrate_prepare_row_test/migrate_prepare_row_test.module b/core/modules/migrate/tests/modules/migrate_prepare_row_test/migrate_prepare_row_test.module
index 1da25f5a6d5cb7ec70e148d76a2784469b005981..6b7bc8c25f025eefc727f36c2f2b3b744e0f9d92 100644
--- a/core/modules/migrate/tests/modules/migrate_prepare_row_test/migrate_prepare_row_test.module
+++ b/core/modules/migrate/tests/modules/migrate_prepare_row_test/migrate_prepare_row_test.module
@@ -21,8 +21,8 @@ function migrate_prepare_row_test_migrate_prepare_row(Row $row, MigrateSourceInt
     // Record mapping but don't record a message.
     throw new MigrateSkipRowException('', TRUE);
   }
-  elseif ($data == 'skip_and_dont_record') {
+  elseif ($data == 'skip_and_do_not_record') {
     // Don't record mapping but record a message.
-    throw new MigrateSkipRowException('skip_and_dont_record message', FALSE);
+    throw new MigrateSkipRowException('skip_and_do_not_record message', FALSE);
   }
 }
diff --git a/core/modules/migrate/tests/modules/migrate_prepare_row_test/src/Plugin/migrate/process/TestSkipRowProcess.php b/core/modules/migrate/tests/modules/migrate_prepare_row_test/src/Plugin/migrate/process/TestSkipRowProcess.php
index 4822113b325459e0dd04188328c83ee64f157c30..b1540888ac1fb7debd165fe1597e20cab5c6b484 100644
--- a/core/modules/migrate/tests/modules/migrate_prepare_row_test/src/Plugin/migrate/process/TestSkipRowProcess.php
+++ b/core/modules/migrate/tests/modules/migrate_prepare_row_test/src/Plugin/migrate/process/TestSkipRowProcess.php
@@ -25,7 +25,7 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
     if ($data == 'skip_and_record (use plugin)') {
       throw new MigrateSkipRowException('', TRUE);
     }
-    elseif ($data == 'skip_and_dont_record (use plugin)') {
+    elseif ($data == 'skip_and_do_not_record (use plugin)') {
       throw new MigrateSkipRowException('', FALSE);
     }
     return $value;
diff --git a/core/modules/migrate/tests/src/Kernel/MigrateSkipRowTest.php b/core/modules/migrate/tests/src/Kernel/MigrateSkipRowTest.php
index c30577eb808c9e3150ab4710a2b5f4242828e5a5..8de7fb2022fdf7e6c06b23d3086db6786818dd52 100644
--- a/core/modules/migrate/tests/src/Kernel/MigrateSkipRowTest.php
+++ b/core/modules/migrate/tests/src/Kernel/MigrateSkipRowTest.php
@@ -33,7 +33,7 @@ public function testPrepareRowSkip() {
         'plugin' => 'embedded_data',
         'data_rows' => [
           ['id' => '1', 'data' => 'skip_and_record'],
-          ['id' => '2', 'data' => 'skip_and_dont_record'],
+          ['id' => '2', 'data' => 'skip_and_do_not_record'],
         ],
         'ids' => [
           'id' => ['type' => 'string'],
@@ -69,7 +69,7 @@ public function testPrepareRowSkip() {
     $messages = $id_map_plugin->getMessages(['id' => 2])->fetchAll();
     $this->assertCount(1, $messages);
     $message = reset($messages);
-    $this->assertEquals('skip_and_dont_record message', $message->message);
+    $this->assertEquals('skip_and_do_not_record message', $message->message);
     $this->assertEquals(MigrationInterface::MESSAGE_INFORMATIONAL, $message->level);
 
     // Insert a custom processor in the process flow.
@@ -80,7 +80,7 @@ public function testPrepareRowSkip() {
     // Change data to avoid triggering again hook_migrate_prepare_row().
     $definition['source']['data_rows'] = [
       ['id' => '1', 'data' => 'skip_and_record (use plugin)'],
-      ['id' => '2', 'data' => 'skip_and_dont_record (use plugin)'],
+      ['id' => '2', 'data' => 'skip_and_do_not_record (use plugin)'],
     ];
     $migration = \Drupal::service('plugin.manager.migration')->createStubMigration($definition);
 
diff --git a/core/modules/search/tests/src/Functional/SearchPageTextTest.php b/core/modules/search/tests/src/Functional/SearchPageTextTest.php
index 6af5f8956f25b93fee9c21c5274c549e1c394f45..219e23e1f56813a252161b6fdf9161b10f4c6d0f 100644
--- a/core/modules/search/tests/src/Functional/SearchPageTextTest.php
+++ b/core/modules/search/tests/src/Functional/SearchPageTextTest.php
@@ -56,7 +56,7 @@ protected function setUp(): void {
   public function testSearchLabelXSS() {
     $this->drupalLogin($this->drupalCreateUser(['administer search']));
 
-    $keys['label'] = '<script>alert("Dont Panic");</script>';
+    $keys['label'] = '<script>alert("Don\'t Panic");</script>';
     $this->drupalPostForm('admin/config/search/pages/manage/node_search', $keys, t('Save search page'));
 
     $this->drupalLogin($this->searchingUser);
diff --git a/core/modules/system/tests/modules/session_test/session_test.routing.yml b/core/modules/system/tests/modules/session_test/session_test.routing.yml
index 25a9321181ea7c5a0ab506a67c5415c6b02ed33f..ba7d08667ca37089df2c64f8fd467b6b005361c9 100644
--- a/core/modules/system/tests/modules/session_test/session_test.routing.yml
+++ b/core/modules/system/tests/modules/session_test/session_test.routing.yml
@@ -66,11 +66,11 @@ session_test.set_message:
   requirements:
     _access: 'TRUE'
 
-session_test.set_message_but_dont_save:
-  path: '/session-test/set-message-but-dont-save'
+session_test.set_message_but_do_not_save:
+  path: '/session-test/set-message-but-do-not-save'
   defaults:
     _title: 'Set message but do not save session'
-    _controller: '\Drupal\session_test\Controller\SessionTestController::setMessageButDontSave'
+    _controller: '\Drupal\session_test\Controller\SessionTestController::setMessageButDoNotSave'
   requirements:
     _access: 'TRUE'
 
diff --git a/core/modules/system/tests/modules/session_test/src/Controller/SessionTestController.php b/core/modules/system/tests/modules/session_test/src/Controller/SessionTestController.php
index 95be208a3ed26d15160400fa6e059dd128e4512b..7acc00dfd8580196786a4eccd362c0470949a223 100644
--- a/core/modules/system/tests/modules/session_test/src/Controller/SessionTestController.php
+++ b/core/modules/system/tests/modules/session_test/src/Controller/SessionTestController.php
@@ -124,7 +124,7 @@ public function setMessage() {
    * @return string
    *   A notification message.
    */
-  public function setMessageButDontSave() {
+  public function setMessageButDoNotSave() {
     \Drupal::service('session_handler.write_safe')->setSessionWritable(FALSE);
     $this->setMessage();
     return ['#markup' => ''];
diff --git a/core/modules/system/tests/src/Functional/Session/SessionTest.php b/core/modules/system/tests/src/Functional/Session/SessionTest.php
index 8388ad5a91c11b4c588e9e7df72c1f1831e55299..49cee1e714f8b7293dee40b09609467768461a11 100644
--- a/core/modules/system/tests/src/Functional/Session/SessionTest.php
+++ b/core/modules/system/tests/src/Functional/Session/SessionTest.php
@@ -213,7 +213,7 @@ public function testEmptyAnonymousSession() {
     $this->assertNull($this->drupalGetHeader('Set-Cookie'), 'New session was not started.');
 
     // Verify that no session is created if drupal_save_session(FALSE) is called.
-    $this->drupalGet('session-test/set-message-but-dont-save');
+    $this->drupalGet('session-test/set-message-but-do-not-save');
     $this->assertSessionCookie(FALSE);
     $this->assertSessionEmpty(TRUE);
 
diff --git a/core/tests/Drupal/KernelTests/Core/Config/ConfigFileContentTest.php b/core/tests/Drupal/KernelTests/Core/Config/ConfigFileContentTest.php
index 515d60ac04273554f42d36baa1d00be83b3b85f5..7e71cf75498f9316c804c52dafd69a2a48f5bc27 100644
--- a/core/tests/Drupal/KernelTests/Core/Config/ConfigFileContentTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Config/ConfigFileContentTest.php
@@ -111,10 +111,10 @@ public function testReadWriteConfig() {
     $this->assertEqual($config->get($nested_array_key), $array_value, 'Nested array configuration value found.');
 
     // Read a top level value that doesn't exist.
-    $this->assertNull($config->get('i_dont_exist'), 'Non-existent top level value returned NULL.');
+    $this->assertNull($config->get('i_do_not_exist'), 'Non-existent top level value returned NULL.');
 
     // Read a nested value that doesn't exist.
-    $this->assertNull($config->get('i.dont.exist'), 'Non-existent nested value returned NULL.');
+    $this->assertNull($config->get('i.do.not.exist'), 'Non-existent nested value returned NULL.');
 
     // Read false value.
     $this->assertFalse($config->get($false_key), "Boolean FALSE value returned the FALSE.");
diff --git a/core/themes/claro/css/components/tabledrag.css b/core/themes/claro/css/components/tabledrag.css
index bf1e73def61cb780d54887098d4adaecd97f7a04..a53f43d8ebf4071cc5afa79740be939a5f261be3 100644
--- a/core/themes/claro/css/components/tabledrag.css
+++ b/core/themes/claro/css/components/tabledrag.css
@@ -92,7 +92,7 @@ body.drag {
   border-bottom: none;
 }
 
-/* Dont display the abbreviation of 'add-new' table rows. */
+/* Don't display the abbreviation of 'add-new' table rows. */
 
 .add-new .tabledrag-changed {
   display: none;
diff --git a/core/themes/claro/css/components/tabledrag.pcss.css b/core/themes/claro/css/components/tabledrag.pcss.css
index 1f95b68087dcf435425c800448f33d86ddb85333..b258d112eb77bb90816d5339e1415782cd6ae83f 100644
--- a/core/themes/claro/css/components/tabledrag.pcss.css
+++ b/core/themes/claro/css/components/tabledrag.pcss.css
@@ -36,7 +36,7 @@ body.drag {
 .tabledrag-changed.tabledrag-changed {
   border-bottom: none;
 }
-/* Dont display the abbreviation of 'add-new' table rows. */
+/* Don't display the abbreviation of 'add-new' table rows. */
 .add-new .tabledrag-changed {
   display: none;
 }