diff --git a/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php b/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php
index 5f25dd7..6ce4115 100644
--- a/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php
+++ b/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php
@@ -57,6 +57,18 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#value' => $this->t('Save'),
     ];
 
+    $form['duplicate_button'] = [
+      '#type' => 'submit',
+      '#name' => 'duplicate_button',
+      '#value' => 'Duplicate button 1',
+    ];
+
+    $form['duplicate_button_2'] = [
+      '#type' => 'submit',
+      '#name' => 'duplicate_button',
+      '#value' => 'Duplicate button 2',
+    ];
+
     return $form;
   }
 
diff --git a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
index 9931804..5e66f86 100644
--- a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
+++ b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
@@ -201,13 +201,13 @@ public function testLegacyFieldAsserts() {
       $this->assertFieldById('edit-name');
       $this->fail('The "edit-name" field with no value was found.');
     }
-    catch (\PHPUnit_Framework_ExpectationFailedException $e) {
+    catch (ExpectationException $e) {
       $this->pass('The "edit-name" field with no value was not found.');
     }
 
-    // Test that the assertion fails correctly if NULL is passed in.
+    // Test that the assertion fails correctly if another value is passed in.
     try {
-      $this->assertFieldById('name', NULL);
+      $this->assertFieldById('edit-name', 'not the value');
       $this->fail('The "name" field was found.');
     }
     catch (ExpectationException $e) {
@@ -237,6 +237,19 @@ public function testLegacyFieldAsserts() {
       $this->pass('The "name" field was found.');
     }
 
+    // Test that multiple fields with the same name are validated correctly.
+    $this->assertFieldByName('duplicate_button', 'Duplicate button 1');
+    $this->assertFieldByName('duplicate_button', 'Duplicate button 2');
+    $this->assertNoFieldByName('duplicate_button', 'Rabbit');
+
+    try {
+      $this->assertNoFieldByName('duplicate_button', 'Duplicate button 2');
+      $this->fail('The "duplicate_button" field with the value Duplicate button 2 was not found.');
+    }
+    catch (ExpectationException $e) {
+      $this->pass('The "duplicate_button" field with the value Duplicate button 2 was found.');
+    }
+
     $this->assertOptionByText('options', 'one');
     try {
       $this->assertOptionByText('options', 'four');