diff -u b/core/modules/block/tests/src/Functional/BlockUiTest.php b/core/modules/block/tests/src/Functional/BlockUiTest.php
--- b/core/modules/block/tests/src/Functional/BlockUiTest.php
+++ b/core/modules/block/tests/src/Functional/BlockUiTest.php
@@ -244,7 +244,7 @@
     // block has one context defined which is not available for it on the
     // Block Layout interface).
     $this->drupalGet('admin/structure/block/add/test_context_aware_no_valid_context_options/classy');
-    $this->assertSession()->fieldNotExists('edit-settings-context-mapping-email', 'The mapping selector is missing as expected.');
+    $this->assertSession()->fieldNotExists('edit-settings-context-mapping-email');
 
     // Test context mapping allows empty selection for optional contexts.
     $this->drupalGet('admin/structure/block/manage/testcontextawareblock');