Jest vs Mocha: Which one Should You Choose?

When it comes to testing JavaScript applications, selecting the right testing framework can significantly impact your development process and overall project success. Among the available options, Jest and Mocha stand out as two popular choices, each with its own set of features and benefits.

In this article we will see what are Unit tests then we will explore more about Jest and Mocha.

What are unit tests?

Before diving into the specifics of Jest and Mocha, let’s briefly review what unit testing.

Unit testing involves isolating components or units of code, such as functions or classes, and passing them to various test cases to verify their behavior. These tests are typically automated and are used to catch bugs and regressions early in the development process.

What is Jest?

Jest is a popular JavaScript testing framework developed by Facebook. It is widely used for testing React applications but can be used for testing any JavaScript codebase.

Features of Jest:

• Zero configuration – you can get started by just installing Jest and using it. You do not require any extra configuration to start testing your code.
• Mocking – To simulate return values from functions, jest provides a robust framework to mock functions’ return values to suit your test cases.
• Snapshot testing – Creates a copy of the produced HTML file and tests if the current version matches that of the previous snapshot.
• Code coverage – Creates a small interactive website that shows you which lines of code were not tested in your test suite.
• Watch mode – The tests re-run if you make changes to your code.

Syntax:

test('description of the test case', () => {
  // Test code goes here
  expect(/* actual value */).toBe(/* expected value */);
});

Example: Let’s have a test file that tests the classic “FizzBuzz”

Javascript

const fizzBuzz = require('./index');

describe("Testing FizzBuzz", () => {
    it("Sending 1 will return '1'", () => {
        expect(fizzBuzz(1)).toBe("1");
    });

    it("Sending 2 will return '2'", () => {
        expect(fizzBuzz(2)).toBe("2");
    });

    it("Sending 3 will return Fizz", () => {
        expect(fizzBuzz(3)).toBe("Fizz");
    });

    it("Sending 4 will return '4'", () => {
        expect(fizzBuzz(4)).toBe("4");
    });

    it("Sending 5 will return Buzz", () => {
        expect(fizzBuzz(5)).toBe("Buzz");
    });

    it("Sending 6 will return Fizz", () => {
        expect(fizzBuzz(6)).toBe("Fizz");
    });

    it("Sending 10 will return Buzz", () => {
        expect(fizzBuzz(10)).toBe("Buzz");
    });

    it("Sending 15 will return FizzBuzz", () => {
        expect(fizzBuzz(15)).toBe("FizzBuzz");
    });

    it("Sending 30 will return FizzBuzz", () => {
        expect(fizzBuzz(30)).toBe("FizzBuzz");
    });
});

What is Mocha

Mocha is a flexible JavaScript testing framework that runs on Node.js and in the browser. It provides a minimalistic testing environment, that allows to choose their preferred assertion libraries and mocking frameworks.

Features of Mocha:

• Mocha is a flexible and extensible testing framework that provides you the freedom to choose your preferred assertion libraries, mocking utilities, and other testing tools.
• It offers a simple and expressive syntax, which makes it easy to write and maintain tests.
• Mocha can be used to test any JavaScript code, regardless of the framework or library being used.
• Unlike Jest, Mocha does not include built-in mocking or assertion libraries but can be easily integrated with popular libraries such as Chai for assertions and Sinon for mocking.

Syntax:

describe('suite description', () => {
  it('test case description', () => {
    // Test code goes here
    assert.equal(/* actual value */, /* expected value */);
  });
});

Example:

Javascript

const fizzBuzz = require('../index');
const assert = require('assert');

describe("Testing FizzBuzz", () => {
    it("Sending 1 will return '1'", () => {
        assert.equal(fizzBuzz(1), "1");
    });

    it("Sending 2 will return '2'", () => {
        assert.equal(fizzBuzz(2), "2");
    });

    it("Sending 3 will return Fizz", () => {
        assert.equal(fizzBuzz(3), "Fizz");
    });

    it("Sending 4 will return '4'", () => {
        assert.equal(fizzBuzz(4), "4");
    });

    it("Sending 5 will return Buzz", () => {
        assert.equal(fizzBuzz(5), "Buzz");
    });

    it("Sending 6 will return Fizz", () => {
        assert.equal(fizzBuzz(6), "Fizz");
    });

    it("Sending 10 will return Buzz", () => {
        assert.equal(fizzBuzz(10), "Buzz");
    });

    it("Sending 15 will return FizzBuzz", () => {
        assert.equal(fizzBuzz(15), "FizzBuzz");
    });

    it("Sending 30 will return FizzBuzz", () => {
        assert.equal(fizzBuzz(30), "FizzBuzz");
    });
});

Difference between Jest and Mocha.

Comparison	Jest	Mocha
Configuration	No need to configure anything	Requires configuration with additional libraries
Performance	Slower because of multiple features in provides	Reported to be 40 times faster due to its light-weight codebase
Snapshot Testing	Built-in support for UI testing	Requires additional libraries and configuration
Code coverage	Built-in support for UI testing	Requires additional libraries and configuration

Conclusion

Jest and Mocha are excellent frameworks used in JavaScript/Node applications. Jest is a closed library that provides out-of-box functionality. At the same time, Mocha is a much lighter library that integrates well with third-party libraries to deliver exactly what you require. For any small project, Jest is perfectly capable and recommended for testing. However, if there is any specific feature you require for your code base that Jest does not offer, it is a great idea to use Mocha for your project.