Express JS Tutorial | Unit Testing

Unit testing is a critical part of developing a software application. It helps to ensure that individual components of the code are working as expected and do not break when changes are made. When it comes to developing web applications using Express JS, unit testing is equally important to ensure the reliability and stability of the application.

Express JS is a popular web application framework for Node.js that provides a robust set of features for building web applications. In this tutorial, we will learn how to perform unit testing in Express JS using various tools and techniques.

Setting Up the Environment

Before we can start with unit testing in Express JS, we need to set up the environment and install the necessary dependencies. First, we need to install the mocha testing framework along with the chai assertion library. These tools will help us write and run unit tests for our Express JS application.

npm install mocha chai --save-dev

Once the testing framework and assertion library are installed, we can start writing unit tests for our Express JS application.

Writing Unit Tests

To write unit tests for an Express JS application, we need to create separate test files for each component of the application. For example, if we have a route for handling user authentication, we can create a separate test file to test the functionality of that route. We can use the mocha testing framework to define test suites and test cases, and the chai assertion library to make assertions about the expected behavior of the code.

const chai = require('chai');
const chaiHttp = require('chai-http');
const app = require('../app');

chai.use(chaiHttp);

describe('User Authentication', () => {
  it('should log in a user', (done) => {
    chai.request(app)
      .post('/login')
      .send({ username: 'john', password: 'secret' })
      .end((err, res) => {
        chai.expect(res).to.have.status(200);
        done();
      });
  });
});

In the example above, we have written a unit test for the user authentication route of our Express JS application. We make a POST request to the /login route with valid credentials and then assert that the response status code is 200, indicating a successful login.

Running Unit Tests

Once we have written the unit tests for our Express JS application, we can run them using the mocha testing framework. We can add a script in the package.json file to run the tests using the mocha command.

"scripts": {
  "test": "mocha"
}

After adding the test script, we can run the unit tests by executing the following command in the terminal:

npm test

The mocha testing framework will execute all the test files in the specified directory and report the results of the test cases. If any test case fails, we can debug and fix the issue in the code to ensure that the unit tests pass successfully.

Conclusion

Unit testing is an essential aspect of developing Express JS applications. It helps to ensure that the code is functioning as expected and does not introduce any regressions when changes are made. By following the steps outlined in this tutorial, you can effectively write and run unit tests for your Express JS application, contributing to the overall reliability and stability of the application.