What is Vitest?

Vitest is a testing library specifically designed for Vite and React applications. It aims to provide a simple and intuitive API for creating and running tests while being highly customizable and extensible.

Here are some key advantages of Vitest :

• Component testing for Vue, React, Svelte, Lit, and more

• Out-of-the-box TypeScript / JSX support

• ESM first, top-level await

• Multi-threading workers

• Filtering, timeouts, concurrent for suite and tests

• Jest-compatible Snapshot

• Chai built-in for assertions + Jest expect compatible APIsDesigned with a Jest-compatible API

How to integrate Vitest in a Vite application

In a Vite project, integrating Vitest can be done by installing the Vitest package as a dev dependency.

npm install -D vitest

I used vite in my current project, so It does not need extra configuration. For projects using Next Js or React, you can add vitest by adding a file vitest.config.ts. All the examples, you may find here.

// vitest.config.ts for Next Js
import { defineConfig } from 'vitest/config'
import react from '@vitejs/plugin-react'

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [react()],
  test: {
    environment: 'jsdom',
  },
})

// vitest.config.ts for Create-React-App
import { defineConfig } from 'vite'

export default defineConfig({
  test: {
    globals: true,
    environment: 'happy-dom',
  },
})

In the package.json, I will add new lines to run testing.

...
"test": "vitest",
"coverage": "vitest run --coverage"
...

Write tests for my application

Here is an example of doing the unit testing of the utils function. it, describe, and expect can be imported from vitest. The describe function is used to group related test cases together. In this case, the description of the test suite is "should doCalculating do calculate correctly". The it function is used to define individual test cases. In this case, the test case is "should handle addition and routing". Inside the test case function, the doComputating function is called with test data, and the result is compared to an expected value using the expect function. The toEqual matcher checks that the result1 value is equal to the expected1 value.

By running this test, we can ensure that the doComputating function handles addition and rounding as expected. Writing test cases like this help to catch bugs and ensure that changes to the codebase do not introduce regressions.

import { it, describe, expect } from "vitest";
import { doComputating } from "../../src/utils/index";

describe.concurrent("should doCalculating do calculate correctly", () => {
  it("should handle addition and rouding", () => {
    const nums1 = [2, 3, 4];
    const ops1 = ["+", "-"];
    const expected1 = 1;
    const result1 = doComputating(nums1, ops1);

    expect(result1).toEqual(expected1);
  });
...
}

If you use .concurrent on a suite as the example, every test in it will be run in parallel. Or if you use .concurrent consecutive tests to run them in parallel.

import { describe, it } from 'vitest'

// The two tests marked with concurrent will be run in parallel
describe('suite', () => {
  it('serial test', async () => { /* ... */ })
  it.concurrent('concurrent test 1', async ({ expect }) => { /* ... */ })
  it.concurrent('concurrent test 2', async ({ expect }) => { /* ... */ })
})

The full code of this blog can be found here.

Thank you for your reading 👋👋👋

References

[1] vitest.dev/guide/features.html