Jorjis Hasan

Posted on Jan 2

Unit & Integration Testing

#webdev #javascript #testing #react

🔥 Fireup Unit and Integration Testing with Jest and Axios

Testing is a vital part of ensuring that your code works as expected and remains reliable over time. This guide explains Unit Testing and Integration Testing with examples using Jest and Axios. By the end of this, you’ll be equipped to write your own tests confidently! 🚀

📚 Introduction to Testing

Testing involves verifying that your code behaves as expected under various conditions. With Jest, a popular testing library, you can write two key types of tests:

Unit Tests: Test individual functions or components in isolation.
Integration Tests: Verify how different parts of your application work together.

These tests help catch bugs early, reduce regression issues, and maintain high code quality. Let’s start by exploring Unit Testing! 🧪

🧪 Unit Testing

Unit Testing focuses on testing individual functions or components in isolation. It ensures each small unit of your code works independently as intended.

Example: Testing a Sum Function

Here’s a simple function that sums two numbers:

// src/sum.js
export const sum = (a, b) => a + b;

Writing the Unit Test

Create a test file src/__tests__/sum.test.js and write the following:

// src/__tests__/sum.test.js
import { sum } from '../sum';

describe('sum', () => {
  it('should add two numbers correctly', () => {
    expect(sum(1, 2)).toBe(3);
    expect(sum(-1, 1)).toBe(0);
  });
});

Running the Unit Test

Run the test with the following command:

npx jest src/__tests__/sum.test.js

If everything works as expected, you’ll see a ✅ confirming that the test passed.

🔗 Integration Testing with Axios

Integration Testing ensures that different parts of your application work well together. Let’s test a function that fetches user data from an API using Axios.

Example: Fetching User Data

Suppose we have a function that retrieves user data from an API:

// src/apiService.js
import axios from 'axios';

export const fetchUserData = async (userId) => {
  const response = await axios.get(`https://jsonplaceholder.typicode.com/users/${userId}`);
  return response.data;
};

Writing the Integration Test

To test this function, create a file src/__tests__/apiService.test.js. We’ll mock Axios to prevent real API calls.

// src/__tests__/apiService.test.js
import axios from 'axios';
import { fetchUserData } from '../apiService';

jest.mock('axios'); // Mocking Axios globally for tests

describe('fetchUserData', () => {
  it('should fetch user data successfully', async () => {
    const mockUserData = { id: 1, name: 'Alice' };
    axios.get.mockResolvedValue({ data: mockUserData });

    const userData = await fetchUserData(1);

    expect(userData).toEqual(mockUserData);
    expect(axios.get).toHaveBeenCalledWith('https://jsonplaceholder.typicode.com/users/1');
  });

  it('should throw an error if fetching fails', async () => {
    axios.get.mockRejectedValue(new Error('Fetch failed'));

    await expect(fetchUserData(1)).rejects.toThrow('Fetch failed');
  });
});

Key Points:

jest.mock('axios'): Mocks the entire Axios library.
mockResolvedValue: Simulates a successful API response.
mockRejectedValue: Simulates an API failure.

Running the Integration Test

Run the test with the following command:

npx jest src/__tests__/apiService.test.js

If successful, Jest will confirm the tests for both success and failure scenarios have passed. ✅

🎉 Conclusion

Unit and Integration Testing are essential tools for building reliable and maintainable applications. By using Jest and Axios, you can:

Validate individual functions with Unit Tests.
Verify interactions between modules with Integration Tests.

Unit and Integration Testing are powerful methods to ensure your code works well individually and collectively. Start adding tests to your codebase today and enjoy the peace of mind that comes with knowing your application is well-tested. Happy coding and testing! 🧑‍💻✨

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