Happo
Visual diffing in CI for user interfaces
...It hooks into your CI environment to compare the visual appearance of UI components before and after a change. Screenshots are taken in different browsers and across different screen sizes to ensure consistent cross-browser and responsive styling of your application. The first thing you want to do is to set up a test suite for Happo. A test suite consists of a set of components and variants of those components. There are many ways to do this, and it all depends on your existing tech stack, your application, your experience with other test frameworks, and more.