vitest-browser-lit

Render Lit components in Vitest Browser Mode. This library follows testing-library principles and exposes only locators and utilities that encourage you to write tests that closely resemble how your Lit components are used.

vitest-browser-lit aims to deliver a good developer experience in Vitest Browser Mode by incorporating the locators API and retry-ability mechanism directly into the render result. This allows you to call user methods without needing to verify the element's existence or wait for external events (like API calls) to render the element.

Requires vitest 4 or higher.

import { render } from 'vitest-browser-lit'
import { expect, test } from 'vitest'
import { html } from 'lit'

test('counter button increments the count', async () => {
  const screen = render(html`<counter-element count="1"></counter-element>`)

  await screen.getByRole('button', { name: 'Increment' }).click()

  await expect.element(screen.getByText('Count is 2')).toBeVisible()
})

vitest-browser-lit also automatically injects render method on the page. Example:

// vitest.config.ts
import { defineConfig } from 'vitest/config'
import { playwright } from '@vitest/browser-playwright'

export default defineConfig({
  test: {
    setupFiles: ['./setup-file.ts'],
    browser: {
      enabled: true,
      provider: playwright(),
      instances: [{ browser: 'chromium' }],
    },
  },
})

// ./setup-file.ts
// add an import at the top of your setup file so TypeScript can pick up types
import 'vitest-browser-lit'

import { page } from 'vitest/browser'
import { test } from 'vitest'
import { html } from 'lit'

test('counter button increments the count', async () => {
  const screen = page.render(html`<counter-element count="1"></counter-element>`)
})

vitest-browser-lit performs cleanup of the component before the test begins, allowing you to see the rendered result in your UI. If you prefer to disable auto-cleanup, you can import the render function from vitest-browser-lit/pure.

Special thanks

• Inspired by @testing-library/react and vitest-browser-react