Tutorial: Testing with Vitest

Learning Objectives and Outcomes

In this tutorial, you will learn how to set up and use Vitest for modern JavaScript testing. By the end of this session, you will be able to:

Understand the basics of test-driven development (TDD) using Vitest.
Set up Vitest in your JavaScript project.
Write and run your first tests efficiently.
Utilize common testing features such as mocking and assertions.
Avoid common pitfalls associated with testing.

Prerequisites and Setup

Before diving into Vitest, ensure that you have the following prerequisites:

Familiarity with basic testing concepts (e.g., what tests are and why they’re important).
A basic understanding of Vite, as Vitest is designed to work seamlessly with it.

Getting Started

Node.js: Ensure you have Node.js installed. You can download it from nodejs.org.
Vite Project: Create a new Vite project if you haven't already:
```
npm create vite@latest my-app
cd my-app
npm install
```
Install Vitest: In your project directory, install Vitest and its dependencies:
```
npm install -D vitest
```

Step-by-Step Instructions with Examples

Step 1: Configure Vitest

Create or modify the vite.config.js file in your project root to include Vitest configuration:

import { defineConfig } from 'vite';
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    globals: true,
    environment: 'jsdom',
  },
});

Step 2: Write Your First Test

Create a new file in the src directory named example.test.js:

import { describe, it, expect } from 'vitest';

describe('Example Test', () => {
  it('should check if true is true', () => {
    expect(true).toBe(true);
  });
});

Step 3: Run Your Tests

To execute your tests, run the following command in your terminal:

npx vitest

You will see the output of your tests in the terminal, indicating whether they passed or failed.

Step 4: Using Mocking

Vitest makes it easy to mock functions. Here's an example:

const myFunction = (num) => num * 2;

describe('Mocking Example', () => {
  it('should mock myFunction', () => {
    const mock = vi.fn(myFunction);
    expect(mock(2)).toBe(4);
    expect(mock).toHaveBeenCalledWith(2);
  });
});

Key Concepts Explained Along the Way

Describe and It: These functions are used to structure your tests. describe groups related tests, and it defines individual test cases.
Expect: This function is used to create assertions. It checks if a value meets certain criteria (e.g., toBe, toEqual).
Mocking: This allows you to simulate functions or modules, providing control over their behavior in tests.

Common Mistakes and How to Avoid Them

Not Configuring Vitest Properly: Ensure your vite.config.js file is correctly set up to avoid runtime errors.
Using Wrong Test Environment: For DOM-related tests, use jsdom as the environment to simulate a browser-like environment.
Forget to Run Tests: Always remember to execute your tests after writing them to ensure they work as intended.

Exercises and Practice Suggestions

Write Additional Tests: Create more test cases for functions in your project to solidify your understanding.
Explore Mocking: Try mocking different functions and modules to see how Vitest can simplify your testing.
Refactor Tests: Look at existing tests in your project and see if they can be improved or simplified using Vitest features.

Next Steps and Further Learning

Explore the Vitest documentation for more advanced features and best practices.
Experiment with integrating Vitest into CI/CD pipelines to automate your testing process.
Consider learning about other testing frameworks to compare and enhance your testing strategies.

By following this tutorial, you’ve taken the first step toward mastering JavaScript testing using Vitest. Happy testing!

Testing with Vitest