diff -u b/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php b/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php
--- b/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php
+++ b/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php
@@ -116,6 +116,10 @@
     $assert_session->assertWaitOnAjaxRequest();
     $this->assertGreaterThan($field_weight_2->getValue(), $field_weight_0->getValue());
     $this->assertGreaterThan($field_weight_1->getValue(), $field_weight_2->getValue());
+
+    // Validate no extraneous widget is displayed.
+    $element = $page->findField('field_unlimited[4][value]');
+    $this->assertEmpty($element);
   }
 
 }