diff -u b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
--- b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
@@ -46,7 +46,7 @@
         $msg_element = $web_assert->waitForElementVisible('css', $selector);
         $this->assertNotEmpty($msg_element, "Message element visible: $selector");
         $web_assert->elementContains('css', $selector, "Msg-$type");
-        $current_messages[$selector] = "Msg-$type";
+        $current_messages[$selector] = ucfirst($type) . " message Msg-$type";
         $this->assertCurrentMessages($current_messages);
       }
       // Remove messages 1 by 1 and confirm the messages are expected.
@@ -60,9 +60,10 @@
     }
 
     $current_messages = [];
-    $nb_messages = count(JsMessageTestCases::getTypes()) * 2;
+    $types = JsMessageTestCases::getTypes();
+    $nb_messages = count($types) * 2;
     for ($i = 0; $i < $nb_messages; $i++) {
-      $current_messages[] = "Msg-$i";
+      $current_messages[] = ucfirst($types[$i % count($types)]) . " message Msg-$i";
     }
     // Test adding multiple messages at once.
     // @see processMessages()
@@ -71,8 +72,12 @@
     $this->click('[id="remove-multiple"]');
     $this->assertCurrentMessages([]);
 
+    $current_messages = [];
+    for ($i = 0; $i < $nb_messages; $i++) {
+      $current_messages[] = "Error message Msg-$i";
+    }
     // The last message is of a different type and shouldn't get cleared.
-    $last_message = 'Msg-' . count($current_messages);
+    $last_message = 'Status message Msg-' . count($current_messages);
     $current_messages[] = $last_message;
     $this->click('[id="add-multiple-error"]');
     $this->assertCurrentMessages($current_messages);