Introduction to Jest

Jest is a delightful JavaScript testing framework maintained by Facebook, designed to ensure correctness in any JavaScript codebase. It is widely used for testing React applications but can also be utilized for testing any JavaScript project.

To install Jest, you can use npm or yarn. Run one of the following commands in your project directory:

npm install --save-dev jest

yarn add --dev jest

Create a test file with a .test.js or .spec.js extension. For example, create a file named sum.test.js:

function sum(a, b) {
    return a + b;
}

module.exports = sum;

Next, add the following test to sum.test.js:

const sum = require('./sum');

test('adds 1 + 2 to equal 3', () => {
    expect(sum(1, 2)).toBe(3);
});

Run your tests using:

npx jest

Jest tests are structured with three main functions:

• describe(): Groups related tests.
• test() or it(): Defines a single test case.
• expect(): Contains the assertion.

Example:

describe('sum function', () => {
    test('adds 1 + 2 to equal 3', () => {
        expect(sum(1, 2)).toBe(3);
    });
});

To write effective tests, consider the following best practices:

• Keep tests isolated and independent.
• Name your tests clearly and descriptively.
• Use beforeEach() and afterEach() for setup and teardown.
• Utilize snapshot testing for UI components.