expressjsHow can I use Jest to test my Express.js application?

Jest is a popular JavaScript testing framework that can be used to test an Express.js application. To get started, install Jest and its Express-compatible adapter, SuperTest.

npm install --save-dev jest supertest

Once installed, create a test file for your Express application. The following example uses app.test.js as the name of the file:

// app.test.js
const request = require('supertest');
const app = require('./app');

describe('Test the root path', () => {
  test('It should response the GET method', async () => {
    const response = await request(app).get('/');
    expect(response.statusCode).toBe(200);
  });
});

The code above imports the request method from the SuperTest package and the Express app from the app.js file. The describe and test methods are used to create a test suite and test case, respectively. The request method is used to make a request to the Express app, and the expect method is used to check the response status code.

To run the test, use the following command:

npm run test

The output should look something like this:

 PASS  app.test.js
  Test the root path
    ✓ It should response the GET method (3ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        2.9s

For more information on using Jest to test an Express application, see the Jest documentation and the SuperTest documentation.

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