Jest - Testing an Express Application

We will set up the Express API to be easily testable. This involves settings up a test environment as well as configuring Jest to work with Node.

Creating a Test Environment

Creating the test environment requires test.env to be added to the config directory. The contents will be identical to dev.env, with the exception of the MongoDB connection string. The test environment should use a separate database such as task-manager-api-test. This will prevent the test cases from messing with development data.

With the environment in place, update the test script to load the enviroment file in. That would be env-cmd ./config/test.env jest --watch.

Configuring Jest

By default, Jest is expecting to run in the browser. You can use Jest with Node, but you’ll need to configure Jest to enable support. Jest can be configured by adding a jest property in pacakage.json. The configuration below sets testEnvironment to node to ensure that Jest runs correctly in Node.js.

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{
  "jest": {
      "testEnvironment": "node"
  }
}

Next, we’ll add tests for the Express API. Each test case will focus on testing a specific endpoint, making assertions about the response from the server.

Testing with Supertest

Supertest allows you to easily test Express apps.

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npm i supertest --save-dev

Now, supertest can be used to test an endpoint. The test case below tests that new users can sign up for accounts. All the account data provided is valid, so a new account should be created.

Step one is to pass the express app to request. Next, supertest methods can be chained together to fit the needs of your tests. post is used to make an HTTP POST request to /users. send is used to send the correct JSON data to the server. expect is used to assert that the response status code is correct. In this case, a successful signup should result in a 201 status code.

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const request = require('supertest')
const app = require('../src/app')

test('Should signup a new user', async () => {
    await request(app).post('/users').send({
        name: "Jay",
        email: "jay@exaple.com",
        password: 'MyPass777!'
    }).expect(201)
})

Ref : The Complete Node.js Dev Course by Andrew Mead