diff -u b/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php b/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php
--- b/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php
+++ b/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php
@@ -131,7 +131,7 @@
 
     $page = $this->getSession()->getPage();
     $page->pressButton("${float_field}_settings_edit");
-    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->waitForElement('css', '.ajax-new-content');
 
     $edit = [
       "fields[${float_field}][settings_edit_form][settings][prefix_suffix]" => TRUE,
@@ -143,7 +143,7 @@
       $page->fillField($name, $value);
     }
     $page->pressButton("${float_field}_plugin_settings_update");
-    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->waitForElement('css', '.field-plugin-summary-cell > .ajax-new-content');
     $this->drupalPostForm(NULL, [], t('Save'));
 
     // Check number_decimal and number_unformatted formatters behavior.
@@ -164,7 +164,7 @@
 
     $page = $this->getSession()->getPage();
     $page->pressButton("${integer_field}_settings_edit");
-    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->waitForElement('css', '.ajax-new-content');
 
     $edit = [
       "fields[${integer_field}][settings_edit_form][settings][prefix_suffix]" => FALSE,
@@ -174,7 +174,7 @@
       $page->fillField($name, $value);
     }
     $page->pressButton("${integer_field}_plugin_settings_update");
-    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->waitForElement('css', '.field-plugin-summary-cell > .ajax-new-content');
     $this->drupalPostForm(NULL, [], t('Save'));
 
     // Check number_integer formatter behavior.