SETUP_JEST_IN_NODEJS.md

SETUP_JEST_IN_NODEJS.md

Node JS TDD (Test Driven Development)

1. Install the following dependencies

     yarn add express mongoose dotenv 

2. Install the following development dependencies

     yarn add nodemon mongodb-memory-server jest supertest -D

3. Generate a basic configuration file of eslint (OPTIONAL)

   Follow the getting started documentation of eslint

   Or execute the next command answering all the questions to make automatically the file eslint for your project

     yarn create @eslint/config
   

   If you have your tests folder into another folder except the root, you have to add the following in eslint.config.js to avoid no-undef errors from ESLint, which doesn't know about the Jest globals. Ej: Into folder src

     .
     .
     .
     {
       files: ["src/tests/**/*"],
       env: {
         jest: true,
       },
     }

4. Generate a basic configuration file of jest

   Follow the getting started documentation of jest

   Or execute the next command answering all the questions to make automatically the file jest for your project

     yarn add babel-jest @babel/core @babel/preset-env -D
     &
     yarn create jest
   

   NOTE: Try to verify the name of you jest file just created, it should be jest.config.mjs (ESM modules)

   If you are using ESModules to import modules, you have to set up babel in your project, so, you have to create the file babel.config.cjs (Recommended) or babel.config.js

     module.exports = {
       presets: [["@babel/preset-env", {targets: {node: "current"}}]],
     };

5. Setting up environment variables for testing with jest

   For this, we need to install dotenv package

       yarn add dotenv

   Then we need to set up this package into the file jest.setup.js just created

       import dotenv from "dotenv";
       import { closeDB, connectDB, getUri } from "./backend/src/config/db";
       import { seederBuilder } from "./backend/src/builder/seeder-builder";
       dotenv.config({ path: ".env.test" });
   
       beforeAll(async () => {
         const uri = await getUri();
         await connectDB({uri});
         await seederBuilder();
       });
   
       afterAll(async () => {
         await closeDB();
       });
   
       console.log({
           PORT: process.env.PORT,
       });

   NOTE: Here we don't need to mock the environment variables because always we work with process.env unlike vite in the frontend

6. Make sure to have this setting up into jest.config.mjs

       .
       .
       .
       setupFilesAfterEnv: ["<rootDir>/jest.setup.js"],

7. This is a basic configuration for your scripts in package.json

     "scripts": {
       "dev": "nodemon server.js",
       "start": "node server.js",
       "test": "jest --watchAll --detectOpenHandles",
       "lint": "yarn eslint"
     }