DOM testing

Bun's test runner plays well with existing component and DOM testing libraries, including React Testing Library and happy-dom.

happy-dom

For writing headless tests for your frontend code and components, we recommend happy-dom. Happy DOM implements a complete set of HTML and DOM APIs in plain JavaScript, making it possible to simulate a browser environment with high fidelity.

To get started install the @happy-dom/global-registrator package as a dev dependency.

$ bun add -d @happy-dom/global-registrator

We'll be using Bun's preload functionality to register the happy-dom globals before running our tests. This step will make browser APIs like document available in the global scope. Create a file called happydom.ts in the root of your project and add the following code:

import { GlobalRegistrator } from "@happy-dom/global-registrator";

GlobalRegistrator.register();

To preload this file before bun test, open or create a bunfig.toml file and add the following lines.

[test]
preload = "./happydom.ts"

This will execute happydom.ts when you run bun test. Now you can write tests that use browser APIs like document and window.

import {test, expect} from 'bun:test';

test('dom test', () => {
  document.body.innerHTML = `<button>My button</button>`;
  const button = document.querySelector('button');
  expect(button?.innerText).toEqual('My button');
});

Depending on your tsconfig.json setup, you may see a "Cannot find name 'document'" type error in the code above. To "inject" the types for document and other browser APIs, add the following triple-slash directive to the top of any test file.

+ /// <reference lib="dom" />

  import {test, expect} from 'bun:test';

  test('dom test', () => {
    document.body.innerHTML = `<button>My button</button>`;
    const button = document.querySelector('button');
    expect(button?.innerText).toEqual('My button');
  });

Let's run this test with bun test:

$ bun test
bun test v1.x

dom.test.ts:
✓ dom test [0.82ms]

 1 pass
 0 fail
 1 expect() calls
Ran 1 tests across 1 files. 1 total [125.00ms]