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Oct 23, 2018
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docs: ✏️ explain how to implement custo getByTestId #207

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41 changes: 41 additions & 0 deletions README.md
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Expand Up @@ -557,6 +557,47 @@ const usernameInputElement = getByTestId('username-input')
> about `data-testid`s from the blog post ["Making your UI tests resilient to
> change"][data-testid-blog-post]

<details>
<summary>What if my project already uses <code>data-test-id</code>? Do I have to migrate to <code>data-testid</code>?
</summary>

`getByTestId` is looking for the `data-testid` attribute and that's not going to
change
[#76](https://github.com/kentcdodds/dom-testing-library/issues/76#issuecomment-406321122)
[#128](https://github.com/kentcdodds/dom-testing-library/issues/128)
[#204](https://github.com/kentcdodds/react-testing-library/issues/204).

What you can do is to create a [custom render](#custom-render) that overwrites
`getByTestId`:

```js
// test-utils.js
import {render} from 'react-testing-library'

const customRender = (node, ...options) => {
const utils = render(node, ...options)

return {
...utils,
getByTestId: id => {
const el = utils.container.querySelector(`[data-test-id="${id}"]`)
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I think it would be good to use the query helpers from dom-testing-library to allow the custom function to support functions, strings, and regex and the exact and preserveWhitespace options in the same way as the other queries:

https://github.com/kentcdodds/dom-testing-library/blob/master/src/query-helpers.js#L36-L47

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@alexkrolick alexkrolick Oct 23, 2018 •
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This could mirror the implementation of the base query:

const queryByTestId = queryByAttribute.bind(null, 'data-test-id')
const queryAllByTestId = queryAllByAttribute.bind(null, 'data-test-id')

function getAllByTestId(container, id, ...rest) {
  const els = queryAllByTestId(container, id, ...rest)
  if (!els.length) {
    throw getElementError(
      `Unable to find an element by: [data-test-id="${id}"]`,
      container,
    )
  }
  return els
}

function getByTestId(...args) {
  return firstResultOrNull(getAllByTestId, ...args)
}

https://github.com/kentcdodds/dom-testing-library/blob/master/src/queries.js#L153-L154

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True, feel fee to make another PR to improve that :) Thanks!

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I used the query helpers in a firs implementation but I was worried the example would go out of sync if the internals for dom-testing-library changed

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Good point. If it's an explicitly exported value, then it should be pretty solid. But if you're importing things from dist then that's probably not safe.

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Query helpers are exported directly for this very use case
https://github.com/kentcdodds/dom-testing-library/blob/master/src/index.js

if (!el) {
throw Error(`Unable to find an element by: [data-test-id="${id}"]`)
}
return el
},
}
}

// re-export everything
export * from 'react-testing-library'

// override render method
export {customRender as render}
```

</details>

#### `asFragment(): DocumentFragment`

Returns a `DocumentFragment` of your rendered component. This can be useful if
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