Jest to test express controllers

Description

How to use jest with Nodejs ES modules to test express controllers. Here you will find how to test asynchronous code and how to use mocks to get rid of side effects.

Note: Babel is used to enable Jest using with ES6 modules.

Setup

To go through it on your own:

1. Initialize your app npm init

2. To use ES modules, add type: "module" to package.json file.

3. Install express, mongoose and jest packages npm install express mongoose jest

4. Initialize jest npm init jest@latest

5. In jest.config.mjs file: de-comment transform key and assign it a value like transform: { "^.+\\.js$": "babel-jest" }. Just be aware that the rejex will depend on the file extensions on your project.

6. Install babel npm i @babel/core @babel/node @babel/preset-env

7. Configure babel by creating .babelrc file in the root folder.

8. Inside .babelrc file write

   {
       "presets": [["@babel/preset-env", { "targets": { "node": "current" } }]]
   }
   

Article

If you have no background in testing, check out this tutorial:

https://www.freecodecamp.org/news/how-to-handle-side-effects-in-jest/