When you're writing tests, you often need to check that values meet certain conditions. expect gives you access to a number of "matchers" that let you validate different things.| jestjs.io
We spent the past year making Jest faster, easier to configure, added tons of features and built snapshot testing. However, there were two areas where we invested very little we can move fast and improve the framework for Facebook and the open source community at light-speed. Jest's goal is to come with batteries included and to require as little configuration as necessary. We recently got a chance to explain our philosophy on a create-react-app issue.| jestjs.io
Snapshot tests are a very useful tool whenever you want to make sure your UI does not change unexpectedly.| jestjs.io