Transcripted Summary
# What is Jest?
Jest is an open sourced JavaScript testing library from Facebook. Its slogan is “Delightful JavaScript Testing”.
Jest is not just a test-runner, it is a complete testing framework that has brought modern testing to another level.
# Why use Jest you ask?
Well, Jest is a breeze to set up.
We will shortly look at the steps in installing Jest.
Jest is also super-fast during execution.
Well, what makes Jest fast? Actually, it's a combination of several factors, including parallelization and running slowest test first. This ensures all cores are utilized to the max.
Jest also does snapshots.
Snapshot testing is amazing. It lets you capture an image that represents your rendered component or response and store it in a file. Then you can compare it later to ensure that the UI or response didn't change.
Jest has it all in one.
It comes with built-in matchers, spies and its own extensive mocking library.
# When would you use Jest?
Well you can use Jest for your unit tests, also API testing with other Javascript libraries like superTest or request-promise.
It can also be used effectively to test against the UI with Puppeteer.
You can even test against some modern DBs like MongoDB and DynamoDB)
