diff --git a/core/modules/aggregator/tests/src/Kernel/AggregatorPluginManagerTest.php b/core/modules/aggregator/tests/src/Kernel/AggregatorPluginManagerTest.php
index 9871a0465eda9f3816540536ff94cc2752c75238..6ddc114d2fe9771c7713ac30c3ca84b0092eb562 100644
--- a/core/modules/aggregator/tests/src/Kernel/AggregatorPluginManagerTest.php
+++ b/core/modules/aggregator/tests/src/Kernel/AggregatorPluginManagerTest.php
@@ -35,7 +35,7 @@ public function testParserInfoAlter() {
     $widget_definition = \Drupal::service('plugin.manager.aggregator.parser')->getDefinition('aggregator_test_parser');
 
     // Test if hook_aggregator_parser_info_alter is being called.
-    $this->assertTrue($widget_definition['definition_altered'], "The 'aggregator_test_parser' plugin definition was updated in in `hook_aggregator_parser_info_alter()`");
+    $this->assertTrue($widget_definition['definition_altered'], "The 'aggregator_test_parser' plugin definition was updated in `hook_aggregator_parser_info_alter()`");
   }
 
   /**
@@ -45,7 +45,7 @@ public function testProcessorInfoAlter() {
     $widget_definition = \Drupal::service('plugin.manager.aggregator.processor')->getDefinition('aggregator_test_processor');
 
     // Test if hook_aggregator_processor_info_alter is being called.
-    $this->assertTrue($widget_definition['definition_altered'], "The 'aggregator_test_processor' plugin definition was updated in in `hook_aggregator_processor_info_alter()`");
+    $this->assertTrue($widget_definition['definition_altered'], "The 'aggregator_test_processor' plugin definition was updated in `hook_aggregator_processor_info_alter()`");
   }
 
 }
diff --git a/core/modules/system/tests/modules/js_message_test/js/js_message_test.es6.js b/core/modules/system/tests/modules/js_message_test/js/js_message_test.es6.js
index e9efaa6ef5de469946fd65a621c9064f8402b77c..e9d910d7ac1ce73227eac4b10e6b271b54a3090f 100644
--- a/core/modules/system/tests/modules/js_message_test/js/js_message_test.es6.js
+++ b/core/modules/system/tests/modules/js_message_test/js/js_message_test.es6.js
@@ -51,7 +51,7 @@
           if (action === 'add') {
             messageObjects[area].indexes[type].push(
               message.add(
-                `This is a message of the type, ${type}. You be the the judge of its importance.`,
+                `This is a message of the type, ${type}. You be the judge of its importance.`,
                 { type },
               ),
             );
@@ -71,7 +71,7 @@
               messageObjects.default.zone.add(
                 `This is message number ${i} of the type, ${
                   testMessages.types[i % testMessages.types.length]
-                }. You be the the judge of its importance.`,
+                }. You be the judge of its importance.`,
                 { type: testMessages.types[i % testMessages.types.length] },
               ),
             );
diff --git a/core/modules/system/tests/modules/js_message_test/js/js_message_test.js b/core/modules/system/tests/modules/js_message_test/js/js_message_test.js
index be3478efc03728d3e62ffee0d04cfcc4acf7a302..cc7644656801e15b04cdce58c86d23590ded39a2 100644
--- a/core/modules/system/tests/modules/js_message_test/js/js_message_test.js
+++ b/core/modules/system/tests/modules/js_message_test/js/js_message_test.js
@@ -36,7 +36,7 @@
         var action = $target.attr('data-action');
 
         if (action === 'add') {
-          messageObjects[area].indexes[type].push(message.add("This is a message of the type, ".concat(type, ". You be the the judge of its importance."), {
+          messageObjects[area].indexes[type].push(message.add("This is a message of the type, ".concat(type, ". You be the judge of its importance."), {
             type: type
           }));
         } else if (action === 'remove') {
@@ -45,7 +45,7 @@
       });
       $('[data-action="add-multiple"]').once('add-multiple').on('click', function () {
         [0, 1, 2, 3, 4, 5].forEach(function (i) {
-          messageObjects.multiple.push(messageObjects.default.zone.add("This is message number ".concat(i, " of the type, ").concat(testMessages.types[i % testMessages.types.length], ". You be the the judge of its importance."), {
+          messageObjects.multiple.push(messageObjects.default.zone.add("This is message number ".concat(i, " of the type, ").concat(testMessages.types[i % testMessages.types.length], ". You be the judge of its importance."), {
             type: testMessages.types[i % testMessages.types.length]
           }));
         });
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
index f83bea8afcb0fe276a09056a846a79fdca8e3e35..ea6a0dedf9c341aa158fec948676569460bee5f7 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
@@ -50,8 +50,8 @@ public function testAddRemoveMessages() {
         $selector = "$messagesSelector .messages.messages--$type";
         $msg_element = $web_assert->waitForElementVisible('css', $selector);
         $this->assertNotEmpty($msg_element, "Message element visible: $selector");
-        $web_assert->elementContains('css', $selector, "This is a message of the type, $type. You be the the judge of its importance.");
-        $current_messages[$selector] = "This is a message of the type, $type. You be the the judge of its importance.";
+        $web_assert->elementContains('css', $selector, "This is a message of the type, $type. You be the judge of its importance.");
+        $current_messages[$selector] = "This is a message of the type, $type. You be the judge of its importance.";
         $this->assertCurrentMessages($current_messages, $messagesSelector);
       }
       // Remove messages 1 by 1 and confirm the messages are expected.
@@ -69,7 +69,7 @@ public function testAddRemoveMessages() {
     $types = JSMessageTestController::getTypes();
     $nb_messages = count($types) * 2;
     for ($i = 0; $i < $nb_messages; $i++) {
-      $current_messages[] = "This is message number $i of the type, {$types[$i % count($types)]}. You be the the judge of its importance.";
+      $current_messages[] = "This is message number $i of the type, {$types[$i % count($types)]}. You be the judge of its importance.";
     }
     // Test adding multiple messages at once.
     // @see processMessages()