diff -u b/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
--- b/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -707,17 +707,10 @@
    *   (optional) A message to display with the assertion.
    */
   protected function assertNoDuplicateIds($message = '') {
-    $args = ['@url' => $this->getUrl()];
-
-    if (!$elements = $this->xpath('//*[@id]')) {
-      $this->fail(new FormattableMarkup('The page @url contains no HTML IDs.', $args));
-      return;
-    }
-
-    $message = $message ?: new FormattableMarkup('The page @url does not contain duplicate HTML IDs', $args);
+    $message = $message ?: new FormattableMarkup('The page @url does not contain duplicate HTML IDs', ['@url' => $this->getUrl()]);
 
     $seen_ids = [];
-    foreach ($elements as $element) {
+    foreach ($this->xpath('//*[@id]') as $element) {
       $id = $element->getAttribute('id');
       if (isset($seen_ids[$id])) {
         $this->fail($message);
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/test_page_test/src/Controller/Test.php
+++ b/core/modules/system/tests/modules/test_page_test/src/Controller/Test.php
@@ -128,4 +128,54 @@ public function metaRefresh() {
     return new RedirectResponse(Url::fromRoute('test_page_test.test_page', [], ['absolute' => TRUE])->toString(), 302);
   }
 
+  /**
+   * Returns a page render array with 2 elements with the same HTML IDs.
+   *
+   * @return array
+   *   A render array as expected by
+   *   \Drupal\Core\Render\RendererInterface::render().
+   */
+  public function renderPageWithDuplicateIds() {
+    return [
+      '#type' => 'container',
+      'title' => [
+        '#type' => 'html_tag',
+        '#tag' => 'h1',
+        '#value' => 'Hello',
+        '#attributes' => ['id' => 'page-element'],
+      ],
+      'description' => [
+        '#type' => 'html_tag',
+        '#tag' => 'h2',
+        '#value' => 'World',
+        '#attributes' => ['id' => 'page-element'],
+      ],
+    ];
+  }
+
+  /**
+   * Returns a page render array with 2 elements with the unique HTML IDs.
+   *
+   * @return array
+   *   A render array as expected by
+   *   \Drupal\Core\Render\RendererInterface::render().
+   */
+  public function renderPageWithoutDuplicateIds() {
+    return [
+      '#type' => 'container',
+      'title' => [
+        '#type' => 'html_tag',
+        '#tag' => 'h1',
+        '#value' => 'Hello',
+        '#attributes' => ['id' => 'page-element-title'],
+      ],
+      'description' => [
+        '#type' => 'html_tag',
+        '#tag' => 'h2',
+        '#value' => 'World',
+        '#attributes' => ['id' => 'page-element-description'],
+      ],
+    ];
+  }
+
 }
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/test_page_test/test_page_test.routing.yml
+++ b/core/modules/system/tests/modules/test_page_test/test_page_test.routing.yml
@@ -90,3 +90,17 @@ test_page_test.meta_refresh:
     _controller: '\Drupal\test_page_test\Controller\Test::metaRefresh'
   requirements:
     _access: 'TRUE'
+
+test_page_test.page_with_duplicate_ids:
+  path: '/test-page-with-duplicate-ids'
+  defaults:
+    _controller: '\Drupal\test_page_test\Controller\Test::renderPageWithDuplicateIds'
+  requirements:
+    _access: 'TRUE'
+
+test_page_test.page_without_duplicate_ids:
+  path: '/test-page-without-duplicate-ids'
+  defaults:
+    _controller: '\Drupal\test_page_test\Controller\Test::renderPageWithoutDuplicateIds'
+  requirements:
+    _access: 'TRUE'
only in patch2:
unchanged:
--- a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
+++ b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
@@ -8,6 +8,7 @@
 use Drupal\Core\Url;
 use Drupal\Tests\BrowserTestBase;
 use Drupal\Tests\Traits\Core\CronRunTrait;
+use PHPUnit\Framework\AssertionFailedError;
 
 /**
  * Tests BrowserTestBase functionality.
@@ -707,4 +708,18 @@ public function testHtkey() {
     $this->assertSession()->statusCodeEquals(403);
   }
 
+  /**
+   * Tests assertNoDuplicateIds() functionality.
+   *
+   * @see \Drupal\Tests\BrowserTestBase::assertNoDuplicateIds()
+   */
+  public function testAssertNoDuplicateIds() {
+    $this->drupalGet(Url::fromRoute('test_page_test.page_without_duplicate_ids'));
+    $this->assertNoDuplicateIds();
+
+    $this->drupalGet(Url::fromRoute('test_page_test.page_with_duplicate_ids'));
+    $this->setExpectedException(AssertionFailedError::class);
+    $this->assertNoDuplicateIds();
+  }
+
 }