diff -u b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
--- b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
+++ b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
@@ -53,11 +53,16 @@
     // tray Ajax activity is done.
     $web_assert->assertWaitOnAjaxRequest();
 
+    // Enable edit mode.
     $this->pressToolbarEditButton();
     $this->assertAnnounceEditMode();
+    // Disable edit mode.
     $this->pressToolbarEditButton();
     $this->assertAnnounceLeaveEditMode();
+    // Enable edit mode again.
     $this->pressToolbarEditButton();
+    // Finally assert that the 'edit mode enabled' announcement is still correct
+    // after toggling the edit mode at least once.
     $this->assertAnnounceEditMode();
   }