protected function DrupalWebTestCase::assertNoDuplicateIds in Drupal 7
Asserts that each HTML ID is used for just a single element.
Parameters
$message: Message to display.
$group: The group this message belongs to.
$ids_to_skip: An optional array of ids to skip when checking for duplicates. It is always a bug to have duplicate HTML IDs, so this parameter is to enable incremental fixing of core code. Whenever a test passes this parameter, it should add a "todo" comment above the call to this function explaining the legacy bug that the test wishes to ignore and including a link to an issue that is working to fix that legacy bug.
Return value
TRUE on pass, FALSE on fail.
2 calls to DrupalWebTestCase::assertNoDuplicateIds()
- AJAXMultiFormTestCase::testMultiForm in modules/simpletest/ tests/ ajax.test 
- Test that a page with the 'page_node_form' included twice works correctly.
- HTMLIdTestCase::testHTMLId in modules/simpletest/ tests/ form.test 
- Tests that HTML IDs do not get duplicated when form validation fails.
File
- modules/simpletest/ drupal_web_test_case.php, line 3834 
Class
- DrupalWebTestCase
- Test case for typical Drupal tests.
Code
protected function assertNoDuplicateIds($message = '', $group = 'Other', $ids_to_skip = array()) {
  $status = TRUE;
  foreach ($this
    ->xpath('//*[@id]') as $element) {
    $id = (string) $element['id'];
    if (isset($seen_ids[$id]) && !in_array($id, $ids_to_skip)) {
      $this
        ->fail(t('The HTML ID %id is unique.', array(
        '%id' => $id,
      )), $group);
      $status = FALSE;
    }
    $seen_ids[$id] = TRUE;
  }
  return $this
    ->assert($status, $message, $group);
}