Even in the biggest web apps built on continuous integration servers with automated deploys, CSS is still often tested only visually. Something can easily be missed or regressions can slip in and not be spotted until production.
As CSS is a declarative language, traditional automated testing techniques either don't apply or aren't sensible. This talk aims to give an overview of the techniques available for automated testing such as page render image diffs, cross-browser equality, frozen DOM structure comparisons. It will also cover some of the tools you can use to integrate automated CSS testing into your build pipeline.