Tests that HTML IDs do not get duplicated when form validation fails.
function testHTMLId() {
$this
->drupalGet('form-test/double-form');
$this
->assertNoDuplicateIds('There are no duplicate IDs');
// Submit second form with empty title.
$edit = array();
$this
->drupalPost(NULL, $edit, 'Save', array(), array(), 'form-test-html-id--2');
$this
->assertNoDuplicateIds('There are no duplicate IDs');
}