Jest

Jest is a simple-to-configure and powerful JavaScript unit testing framework that is built on top of the popular Jasmine framework. Jasmine has been around for a very long time, and is a mature, fully featured, and widely used testing framework. Jest enhances Jasmine by making it easier to configure, as well as providing a wealth of extra features. Jest tests can also be run concurrently, which significantly speeds up the length of time a test suite will take to run. Jest is available through npm, and will therefore require an npm environment, which can be created as follows:

npm init

Here, we have initialized an npm project and can now install the required Jest packages, as follows:

npm install jest --save-dev

With Jest installed, we can either run it using the command npx jest, or we can modify our package.json file to specify that Jest will be used when we run npm test. Let's update our package.json file as follows:

{
  "name": "src...