Diffy and visual regression testing

I recently recorded an episode of Beyond Blocks with Yuri Gerasymov, who runs Diffy.

He and I discussed visual regression testing, why you'd use it, and some features Diffy offers.

I usually write a combination of browser, kernel and unit tests within an application framework like Drupal and Symfony or behavioural tests with Behat.

These validate that my logic works as expected and that functions return the correct results or pages return the correct response codes and content.

There are types of issues, though, such as breakages within the page layout or structure, which these tests won't discover but can be identified by visual regression tests that compare before and after screenshots.

I added to my website during the recording and can see what value it offers as an additional layer of testing on top of the tests I already write.