Why Vitest Might Be Better Than Jest for Your JavaScript Projects

by Dennis — 9 minutes

If you're working on a JavaScript project, you've likely come across Jest, the go-to testing framework for many developers. But there's a new player in town called Vitest, and it’s making waves, especially for those using Vite. Let’s dive into why Vitest might be the better choice for your next project.

What is Vitest?

Vitest is a modern testing framework designed to work seamlessly with Vite, a super-fast build tool and development server. It's all about speed and simplicity, making it an appealing alternative to Jest.

Why Vitest Could Be Better

1. Blazing Fast Performance

Vitest leverages Vite’s fast Hot Module Replacement (HMR) and caching capabilities, making it incredibly fast. If performance is a priority, especially during development, Vitest’s speed is a game-changer.

2. Seamless Integration with Vite

Vitest is built to work perfectly with Vite, which means less configuration and more straightforward setup. If your project uses Vite, integrating Vitest is almost effortless, allowing you to focus more on writing tests and less on configuring your tools. According to the Vitest documentation, Vitest follows Vite's zero-config philosophy, meaning many projects won't need any specific Vitest configuration.

3. Lightweight and Minimalist

Vitest focuses on providing essential features without unnecessary bloat. This makes it easier to use and keeps your testing setup simple. It's ideal for projects where you don’t need the extensive feature set that Jest offers.

4. Great TypeScript Support

Vitest has excellent support for TypeScript out of the box, providing type-safe testing without additional configuration. This can save time and reduce the friction often encountered when setting up TypeScript with other testing frameworks.

Comparing Vitest and Jest

Performance

Vitest outshines Jest in terms of speed. Thanks to its integration with Vite, Vitest benefits from fast reloads and efficient caching, making it significantly faster both in setup and during development cycles. Jest, while robust, can be slower due to its heavier feature set and configuration needs. For developers prioritizing quick feedback and rapid iteration, Vitest provides a noticeably better experience.

Ecosystem and Community

While Jest has been around longer and has a larger community and plugin ecosystem, Vitest is quickly catching up. Vitest offers compatibility with most of the Jest API and ecosystem libraries, so in most projects, it should be a drop-in replacement for Jest. This means that you can leverage the familiarity and maturity of Jest’s ecosystem while benefiting from the speed and simplicity of Vitest. The growing community around Vitest is active and rapidly producing new plugins and resources, making it an increasingly viable option for all types of projects.

Feature Set

Jest is known for its comprehensive feature set, including advanced capabilities like snapshot testing, powerful mocking and spying tools, and detailed coverage reports. However, Vitest covers all essential features effectively and does so with a minimalist approach that avoids unnecessary bloat. For many developers, this translates to a simpler, faster setup that doesn’t compromise on functionality. Additionally, Vitest’s compatibility with Jest APIs means that you can still perform tasks like snapshot testing and mocking with ease.

Vitest focuses on providing a streamlined, enjoyable developer experience, reducing the complexity and overhead associated with testing. This emphasis on developer experience, combined with its speed and seamless integration with Vite, makes Vitest a compelling choice for modern JavaScript projects.

Efficient Testing in Monorepos with Vitest

What’s a Monorepo?

A monorepo is a single repository that contains multiple projects or packages. This setup can simplify dependency management and code sharing between projects, making it easier to maintain consistency and streamline development.

Vitest in a Monorepo

Vitest works excellently in a monorepo setup, especially if you’re using Vite across your projects. By leveraging Vite’s performance optimizations, Vitest can efficiently handle testing across multiple packages, ensuring quick feedback loops and streamlined testing processes.

Vitest Workspaces

Vitest introduces a feature called Workspaces, which is specifically designed to support monorepo environments. Workspaces allow you to run tests across multiple projects within the same repository seamlessly. This means you can manage and execute tests for different packages from a single configuration, saving time and reducing redundancy.

Using Tools like Turborepo

While there are various tools to manage monorepos, Turborepo is a high-performance option that helps speed up builds and simplifies dependency management. Turborepo can work alongside Vitest to optimize your testing setup, ensuring efficient test runs and minimizing redundant tasks.

Why Choose Vitest for Monorepos?

  • Speed: Vitest’s performance is a significant advantage in a monorepo context, where fast feedback loops are crucial.
  • Simplicity: Its minimalist setup means less configuration and easier management of multiple projects.
  • Consistency: Using Vitest with Vite across your monorepo ensures consistent tooling and setup, making it easier to manage and maintain.
  • Workspaces: Vitest Workspaces streamline testing in monorepos, allowing you to run tests across multiple packages from a unified configuration.

By choosing Vitest for your monorepo, you benefit from a faster, simpler, and more integrated testing experience that keeps your development workflow efficient and enjoyable.

Compatibility Between Jest and Vitest Tests

Migrating from Jest to Vitest

One of the great things about Vitest is its compatibility with Jest. Many tests written for Jest can run on Vitest with minimal or no changes. This makes it easier to migrate existing projects to Vitest without having to rewrite all your tests. The Vitest documentation also provides a detailed guide on how to migrate from Jest to Vitest.

Key Compatibility Points

  • Syntax and APIs: Vitest uses similar syntax and APIs to Jest, so functions like describe, it, and expect work in both frameworks. This means that your existing test files can often be reused with little modification.
  • Mocking: Vitest provides mocking capabilities similar to Jest, allowing you to mock functions, modules, and timers in a familiar way.
  • Snapshot Testing: If you're using snapshot testing in Jest, you can continue to do so in Vitest with its compatible snapshot feature.

Potential Adjustments

While Vitest strives for compatibility, there might be some edge cases where adjustments are needed:

  • Custom Matchers: If you use custom matchers or plugins specific to Jest, you might need to find or create equivalents for Vitest.
  • Configuration: Some Jest-specific configurations may need to be adapted for Vitest. This typically involves updating configuration files or changing specific settings to match Vitest’s requirements.

Migration Examples

Similar Syntax and APIs

Vitest and Jest share similar syntax and APIs for defining and running tests. Here’s a basic example of a test written in Jest:

// Jest test example
describe("Math operations", () => {
  test("Adding 1 + 1 equals 2", () => {
    expect(1 + 1).toBe(2);
  });

  test("Multiplying 2 * 3 equals 6", () => {
    expect(2 * 3).toBe(6);
  });
});

The same test can be migrated to Vitest without any changes:

// Vitest equivalent test
import { describe, test, expect } from "vitest";

describe("Math operations", () => {
  test("Adding 1 + 1 equals 2", () => {
    expect(1 + 1).toBe(2);
  });

  test("Multiplying 2 * 3 equals 6", () => {
    expect(2 * 3).toBe(6);
  });
});

As you can see, the describe, test, and expect functions are used identically in both frameworks, ensuring a smooth transition for your test suites.

Mocking and Assertions

Vitest provides similar capabilities for mocking and assertions as Jest. For example, mocking a function in Jest looks like this:

// Jest mock example
const myMockFunction = jest.fn();
myMockFunction.mockReturnValue("mocked");

test("mock function returns mocked value", () => {
  expect(myMockFunction()).toBe("mocked");
});

In Vitest, the same mocking can be achieved with minimal changes:

// Vitest equivalent mock
import { test, mock } from "vitest";

const myMockFunction = mock.fn();
myMockFunction.mockReturnValue("mocked");

test("mock function returns mocked value", () => {
  expect(myMockFunction()).toBe("mocked");
});

Snapshot Testing

Snapshot testing in Jest captures the current state of a component and compares it against a previously stored snapshot. Vitest supports snapshot testing similarly:

// Jest snapshot example
import React from "react";
import renderer from "react-test-renderer";
import MyComponent from "./MyComponent";

test("renders correctly", () => {
  const tree = renderer.create(<MyComponent />).toJSON();
  expect(tree).toMatchSnapshot();
});

Migrating this to Vitest involves using Vitest's snapshot functionality:

// Vitest snapshot example
import { test, snapshot } from "vitest";
import React from "react";
import { createRenderer } from "vitest-snapshot";
import MyComponent from "./MyComponent";

test("renders correctly", () => {
  const renderer = createRenderer();
  const tree = renderer.render(<MyComponent />);
  snapshot(tree).toMatch();
});

Step-by-Step Migration Guide

Here’s a step-by-step example of migrating a Jest test suite to Vitest:

  1. Install Vitest: Add Vitest to your project using your package manager.

  2. Update Test Configuration: Update your test configuration to use Vitest instead of Jest, typically in your package.json or a dedicated test configuration file.

  3. Modify Test Files:

    • Replace import { describe, test, expect } from 'jest'; with import { describe, test, expect } from 'vitest';.
    • Adjust any Jest-specific APIs or configurations to their Vitest equivalents.

  4. Run Tests: Start running your existing tests with Vitest and fix any compatibility issues that arise.

  5. Verify and Adjust: Ensure all tests pass as expected. Make adjustments for any specific differences between Jest and Vitest.

Conclusion

While Jest remains a powerful and versatile testing framework, Vitest’s speed, simplicity, and seamless integration with Vite make it a compelling choice, especially for modern JavaScript projects and those using Vite. If you prioritize performance and ease of use, Vitest might just be the better option for your next project. Plus, with its compatibility with Jest, migrating to Vitest is smoother than you might think. Give it a try and experience the difference for yourself!

References

Here are some useful reference links for learning more about Vitest and Jest:

Vitest

Jest

meerdivotion

Cases

Blogs

Event