diff --git a/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
index 796360f..0e230a4 100644
--- a/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
+++ b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
@@ -57,7 +57,7 @@ public function testForm() {
     $this->assertSession()->elementExists('css', 'form#form-test-form-test-object');
     $this->assertSession()->fieldExists('bananas');
 
-    $edit = ['bananas' => 'green'];
+    $edit = ['bananas' => 'green', 'strawberry' => 'bar'];
     $this->submitForm($edit, 'Save', 'form-test-form-test-object');
 
     $config_factory = $this->container->get('config.factory');
diff --git a/core/modules/system/tests/modules/form_test/src/FormTestObject.php b/core/modules/system/tests/modules/form_test/src/FormTestObject.php
index 5fb0dae..5beb90b 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestObject.php
@@ -34,6 +34,10 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#type' => 'textfield',
       '#title' => $this->t('Bananas'),
     );
+    $form['strawberry'] = [
+      '#type' => 'hidden',
+      '#value' => 'foo',
+    ];
 
     $form['actions']['#type'] = 'actions';
     $form['actions']['submit'] = array(