shadow-dom-testing-library

Why?

Currently, DOM-testing-library does not support checking shadow roots for elements. This can be troublesome when you're looking for something with a "button" that's nested inside a shadowRoot.

https://github.com/testing-library/dom-testing-library/issues/413

Prior art

https://github.com/Westbrook/dom-testing-library

testing-library__dom is a hard fork of DOM testing library which presents its own set of challenges. shadow-dom-testing-library looks to augment the existing functionality.

Preinstallation

Make sure you are using a library which supports rendering shadow roots. For Jest users, this means ensuring you have JSDOM >= 16.2 and Jest >= 26.2

Installation

npm install -D shadow-dom-testing-library

Example usage

// my-button.jsx
export default () => <sl-button>I get wrapped by a button in the shadowRoot!</sl-button>

// my-button.test.jsx
import { render } from "@testing-library/react"
import { screen } from "shadow-dom-testing-library"
import Button from "./my-button"

test("Find the button in the shadow root", async () => {
  render(<Button />)
  const btn = await screen.findByShadowRole("button")
  expect(btn).toBeInTheDocument()
})

API

All queries found here: https://testing-library.com/docs/queries/about/#priority are implemented with a "Shadow" prefix prior to the query type.

API examples

import { render } from "@testing-library/react"
import { getByShadowRole, findByShadowLabelText, queryAllByShadowTitle } from "shadow-dom-testing-library"

test("Find the button", () => {
  const { container } = render(<Button />)

  getByShadowRole(container, "button")
  await findByShadowLabelText(container, /Car Manufacturer/i)
  queryAllByShadowTitle(container, "delete")
})

Usage with screen

Shadow dom testing library ships its own "screen" that you're familiar with. It has all the <ByShadow> functions prebound to the document.

import { render } from "@testing-library/react"
import { screen } from "shadow-dom-testing-library"

test("Lets test some rendering", () => {
  render(<Button />
  screen.getByShadowRole("button")
  await screen.findByShadowLabelText(/Car Manufacturer/i)
  screen.queryAllByShadowTitle("delete")
})

In addition, every <ByShadow> function also accepts a "shallow" option. The shallow option means to only go 1 shadowRoot deep. Perhaps in the future a "recurseDepth" will be implemented to specify shadowRoot depth recursion.

import { render } from "@testing-library/react"
import { screen, getByShadowRole } from "shadow-dom-testing-library"

test("Lets test some rendering", () => {
  render(<Button />)
  getByShadowRole(document, "button", { shallow: true })
  await screen.findByShadowLabelText(/Car Manufacturer/i, { shallow: true })
  screen.queryAllByShadowTitle("delete", { shallow: true })
})

Additional APIs

Shadow DOM testing library also ships its own "deepQuerySelector" and "deepQuerySelectorAll" functions for if you need more fine-grained access to the DOM.

import { deepQuerySelector, deepQuerySelectorAll } from "shadow-dom-testing-library"

const elements = deepQuerySelectorAll(document, "my-button")
const element = deepQuerySelector(document, "my-button", { shallow: true })

Caution

Be careful with the shadowQueries and deepQueries. These functions recurse through every shadow root which can easily lead to unintended elements being found in your tests.

Also, this library is very new, use with caution. Feel free to report any issues.

Performance

Recursing through the Shadow DOM can be expensive if you render a large number of elements in an element. Benchmarks have not been measured, but it will easily be much worse than a regular querySelector call.

Additional notes

Shadow queries will work for both Light DOM and for Shadow DOM elements. For example you can search for a "button" in the Light DOM.

Example of light dom query

function SimpleButton () {
  const [count, setCount] = React.useState(0)

  return (
    <button onClick={() => setCount(count + 1)}>
      {count}
    </button>
  );
}


import { screen } from "shadow-dom-testing-library"

test("Regular buttons should also work with shadow query", async () => {
  render(<SimpleButton />)
  fireEvent.click(await screen.findByRole('button'))
  const el = await screen.findByText(/1/)
  expect(el).toBeInTheDocument()
})

Changelog

1.1.6 (2022-09-30)

• Fixed metadata on npmjs.com

Bug Fixes

• add urls to package.json (d61cfa0)
• add urls to package.json (ae36ba8)