Change record status: 
Project: 
Introduced in branch: 
9.1.x
Introduced in version: 
9.1.0-alpha1
Description: 

The pageContainsNoDuplicateId() assert was added to WebAssert. It asserts that each HTML ID is used for just a single element on the page.

Can be used in BrowserTestBase and WebDriverTestBase tests.

$this->assertSession()->pageContainsNoDuplicateId();
Impacts: 
Module developers