Testing Library
Run locally for transcripts
๐จโ๐ผ We have a component that renders a list of error messages. Let's write
one test that verifies this renders properly.
As a reminder, here's an example of a test with
@testing-library/react:/**
* @vitest-environment jsdom
*/
import { expect, test } from 'vitest'
import { Counter } from './counter.tsx'
test('counter increments when clicked', async () => {
await render(<Counter />)
const button = screen.getByRole('button', { name: /count:/i })
expect(button.textContent).toBe('Count: 0')
await userEvent.click(button)
expect(button.textContent).toBe('Count: 1')
})
Let's start with the most basic use case:
shows nothing when given an empty list
Asserting non-existence
Before you jump in on this one, you should know that Testing Library consists of
a number of utilities that help you find elements in the DOM. The most common
one is
getByRole, which we've used in the example above. But there are several
others you can use. You can read about them in detail in the
Testing Library "About Queries" documentation.In this exercise, we need to discover how to find elements that don't exist in
the DOM. And since we're looking for multiple elements, we can use the
queryByRole method. This
method will return an empty array if no elements are found (which is what we're
looking for).In fact, the only situation where you ever use
queryBy* or queryAllBy*
queries is when you're trying to assert on non-existence of elements. Otherwise,
you should be using the other variants (get* or find*). For more details,
refer to the docs.Utilities
Testing Library comes with a few utilities you may find handy when developing
your tests. If you ever want to know what the DOM looks like at any time, you
can run
screen.debug() and it will log out the current DOM (formatted and with
syntax highlighting).And if you want to play around with that DOM in a real browser, you
screen.logTestingPlaygroundURL() and it will log a URL you can use to open up
the current DOM in testing-playground.com.
This can be pretty handy when you're trying to figure out how to write a query
to find an element.Let's get started!
npx vitest error-list