diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php
index a14e08b2e5..2255ad6540 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php
@@ -47,11 +47,27 @@ public function testBlockForms() {
     $this->drupalPlaceBlock('ajax_forms_test_block');
 
     $this->drupalGet('');
-    $this->drupalPostAjaxForm(NULL, ['test1' => 'option1'], 'test1');
-    $this->assertOptionSelectedWithDrupalSelector('edit-test1', 'option1');
-    $this->assertOptionWithDrupalSelector('edit-test1', 'option3');
-    $this->drupalPostForm(NULL, ['test1' => 'option1'], 'Submit');
-    $this->assertText('Submission successful.');
+    $session = $this->getSession();
+
+    // Select first option and trigger ajax update.
+    $session->getPage()->selectFieldOption('edit-test1', 'option1');
+    $this->assertSession()->assertWaitOnAjaxRequest();
+
+    // Confirm option1 has been selected.
+    $page = $session->getPage();
+    $opt1_selector = $page->find('xpath', '//select[@data-drupal-selector="edit-test1"]//option[@value="option1"]');
+    $this->assertNotEmpty($opt1_selector);
+    $this->assertTrue($opt1_selector->isSelected());
+
+    // Confirm option 3 exists.
+    $opt3_selector = $page->find('xpath', '//select[@data-drupal-selector="edit-test1"]//option[@value="option3"]');
+    $this->assertNotEmpty($opt3_selector);
+
+    // Confirm success message appears after a submit.
+    $page->findButton('edit-submit')->click();
+    $this->assertSession()->waitForButton('edit-submit');
+    $updated_page = $session->getPage();
+    $updated_page->hasContent('Submission successful.');
   }
 
   /**
@@ -65,7 +81,12 @@ public function testQueryString() {
 
     $url = Url::fromRoute('entity.user.canonical', ['user' => $this->rootUser->id()], ['query' => ['foo' => 'bar']]);
     $this->drupalGet($url);
-    $this->drupalPostAjaxForm(NULL, ['test1' => 'option1'], 'test1');
+
+    $session = $this->getSession();
+    // Select first option and trigger ajax update.
+    $session->getPage()->selectFieldOption('edit-test1', 'option1');
+    $this->assertSession()->assertWaitOnAjaxRequest();
+
     $url->setOption('query', [
       'foo' => 'bar',
       FormBuilderInterface::AJAX_FORM_REQUEST => 1,