Jest is test runner for javascript. It is best to install jest per project. You will need to install NodeJS and have a package.json in your root directory.
This command will install jest into your project. Make sure you have a package.json in your project and NodeJS installed.
npm install -D jest @types/jest @babel/preset-envThis project is an example of using jest. You put your test files in the __tests__ directory and import the functions you wish to test. Add assertions to your code using the expect function. If the function does not return as expected, there will be an error after running the command.
Run Jest on the command line.
npm exec jestUse the vscode extension (Jest Runner) found by searching the id firsttris.vscode-jest-runner. This extension will add a run or debug icon above each test to execute them individually.
Jest has a solid open source community. You can find many answers by looking through the GitHub issues https://github.com/facebook/jest or looking through their documentation at https://jestjs.io/