🧪 Testing & Frameworks

 🧪 What is Testing?

Testing is the process of checking whether your application works as expected. It helps you:

Catch bugs early

Ensure code quality

Prevent regressions (bugs that come back)

Gain confidence in deploying changes

🧰 Types of Testing

Type Description Example Tool

Unit Testing Test individual functions/components Jest, Mocha

Integration Test multiple parts working together Supertest, Chai

End-to-End (E2E) Test full workflows like a user would Cypress, Playwright

Manual Testing Click and test the UI manually No tools (human check)

API Testing Verify backend APIs respond correctly Postman, Insomnia

⚙️ Testing in MERN Stack

1. Node.js + Express (Backend)

Frameworks & Tools:

Jest – Testing framework

Supertest – HTTP assertions for API testing

Mocha & Chai – Alternatives to Jest

Example:

js

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// app.test.js

const request = require('supertest');

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

test('GET /api/upload should return 200', async () => {

  const res = await request(app).get('/api/upload');

  expect(res.statusCode).toBe(200);

});

2. React (Frontend)

Frameworks & Tools:

Jest – Built into Create React App

React Testing Library (RTL) – Test components as users would use them

Cypress – For full end-to-end browser tests

Example:

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// FileUpload.test.js

import { render, screen } from '@testing-library/react';

import FileUpload from './FileUpload';

test('renders upload button', () => {

  render(<FileUpload />);

  const button = screen.getByText(/upload/i);

  expect(button).toBeInTheDocument();

});

3. MongoDB (Database)

Use in-memory databases like mongodb-memory-server for fast and isolated tests.

Mock or stub DB calls using tools like Sinon or Jest Mocks.

Example:

js

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// Mocking MongoDB call

jest.mock('../models/File', () => ({

  create: jest.fn().mockResolvedValue({ filename: 'test.jpg' })

}));

🔄 Test Automation Workflow (Example)

Write test files alongside your code.

Run tests locally using npm test.

Use CI/CD pipelines (like GitHub Actions or Jenkins) to run tests automatically on push.

Fix failing tests before deploying.

✅ Best Practices

Write small, focused tests (test one thing at a time)

Use mocking to isolate components and services

Automate your tests in CI/CD

Keep test coverage high, but meaningful

Name tests clearly to describe what’s being tested

🚀 Summary

Testing improves code quality and reliability

Use Jest and Supertest for Node.js APIs

Use React Testing Library or Cypress for frontend tests

Keep tests fast and meaningful

Learn Selenium Python Training in Hyderabad

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