Before we start the config we need to now some things:

Why test my app? 🤔

To make your service scalable, and more consistent!

What is jest? 💭

Because is the most complete and easy to use!

First of all you need to installing the packages below on your project:

• Jest the test framework:

  yarn add jest -D

• jest types is a inteliscense to use jest:

  yarn add @types/jest -D

• Supertest is a framework to simulate http requisitions:

  yarn add supertest -D

Now we need to make initial jest config.

To do that we execute the command below:

  yarn jest --init

After that the console make some questions to you, you need to answer like the image below:

Now you will find a file called "jest.config.js" on your root project.

The next step is ajust this config file like below:

• Bail is the option we set to define the number of errors that make the tests break, in this case i always like to set one:

 bail: 1,

• Clearmocks is the option that clear mocks after tests, this option we set true:

clearMocks: true,

• collectCoverage this option enable or disable the coe coverage, i like to set as true:

collectCoverage: true,

• collectCoverageFrom this option define the path or file s to collect the coverage, usually i set the path where stay my business logic:

collectCoverageFrom: [
    'src/app/Controllers/*.js',
  ],

• coverageDirectory is the place where jest can put the coverage result, i usualy put coverage inside the test folder:

 coverageDirectory: '__tests__/coverage',

• coverageReporters this option set the type of reporters for coverage result, i like to user reports below:

 coverageReporters: ['text', 'lcov', 'json'],

• testMatch this option set the test files extensions:

  testMatch: ['**/__tests__/**/*.test.js'],

Now we can create the folder structure as the image below:

And that is it, now you reandy to starting test your api with jest!