Mocha #

Mocha is a versatile JavaScript testing framework commonly used for testing Node.js applications. It provides a flexible and feature-rich environment for writing and executing tests. Below is a basic overview of using Mocha in a Node.js application:

Installation: #

Install Mocha as a development dependency:

npm install --save-dev mocha

Creating a Simple Test: #

Create a test file (e.g., sum.test.js):

const assert = require('assert');

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

describe('Sum Function', () => {
    it('should return the sum of two numbers', () => {
        assert.strictEqual(sum(1, 2), 3);
    });
});

This test checks if the sum function correctly adds 1 and 2 to equal 3.

Running Tests: #

Run Mocha tests using the command:

npx mocha

Mocha will discover and execute tests, providing results in the console.

Assertions and Matchers: #

Mocha works well with various assertion libraries; here, we’re using Node.js’s built-in assert module:

const assert = require('assert');

assert.strictEqual(sum(2, 2), 4);

Alternatively, you can use assertion libraries like Chai for more expressive assertions.

Testing Asynchronous Code: #

Mocha supports testing asynchronous code using callback functions or Promises:

function fetchData(callback) {
    setTimeout(() => callback('data'), 100);
}

describe('Async Function', () => {
    it('should fetch data asynchronously', (done) => {
        fetchData((data) => {
            assert.strictEqual(data, 'data');
            done();
        });
    });
});

Hooks: #

Mocha provides hooks for setup and teardown:

describe('Test Suite', () => {
    before(() => {
        // Setup code
    });

    after(() => {
        // Teardown code
    });

    beforeEach(() => {
        // Code to run before each test
    });

    afterEach(() => {
        // Code to run after each test
    });

    it('Test Case', () => {
        // Test code
    });
});

Specifying Tests with “it” and “describe”: #

Organize tests using the describe and it functions:

describe('Math Operations', () => {
    it('should add two numbers', () => {
        // Test code
    });

    it('should subtract two numbers', () => {
        // Test code
    });
});

Skipping and Focusing Tests: #

Skip or focus on specific tests using skip and only:

describe('Test Suite', () => {
    it.skip('skipped test', () => {
        // Test code
    });

    it.only('focused test', () => {
        // Test code
    });
});

Running Tests in Watch Mode: #

Run tests in watch mode for continuous testing during development:

npx mocha --watch

Mocha will re-run tests whenever files change.

Running Tests in Parallel: #

Mocha supports running tests in parallel:

npx mocha --parallel

This can significantly speed up test execution for large test suites.

Mocha’s flexibility, rich feature set, and compatibility with various assertion libraries make it a popular choice for testing Node.js applications. Whether testing synchronous or asynchronous code, setting up hooks for setup and teardown, or organizing tests into suites, Mocha provides an intuitive and developer-friendly testing environment.