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119 lines
4.1 KiB
119 lines
4.1 KiB
# jest-expo
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A [Jest](https://facebook.github.io/jest/) preset to painlessly test your Expo / React Native apps.
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### Installation
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- To install the compatible version of `jest-expo` and `jest` for your project, run: `expo install jest-expo jest`.
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- Add the following config to `package.json`:
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```json
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"scripts": {
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...
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"test": "jest"
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},
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"jest": {
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"preset": "jest-expo"
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}
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```
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- Create a `__tests__` directory anywhere you like and a `Example-test.js` file inside of it, and add this code:
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```js
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it('works', () => {
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expect(1).toBe(1);
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});
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```
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- Run `npm test` and it should pass
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> You can use a different version of `jest` than the one that is installed with `expo install`, but keep in mind that the SDK and `jest-expo` are built against that version.
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## Platforms
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You can use `jest-expo` to test any Expo supported platform. For legacy purposes `jest-expo` runs your tests in the standard React Native environment (iOS).
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The recommended way to test your project is with `jest-expo/universal` which runs your tests with every Expo supported platform. Currently this includes iOS, Android, web, and Node (which is used for testing SSR compliance).
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Pressing **X** will open a platform-selection dialog that you can use to test individual platforms. You can also create a custom Jest config and combine the individual platforms with `jest-expo/ios`, `jest-expo/android`, `jest-expo/web`, and `jest-expo/node`.
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### Snapshots
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Because a test is run with multiple different platforms, `jest-expo` saves snapshots using the name of the platform as the extension. This is very useful for testing something like view styles, which are computed differently across web and native.
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Here is an example output:
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|- `View-test.tsx`
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|-- `__snapshots__/View-test.tsx.snap.android`
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|-- `__snapshots__/View-test.tsx.snap.ios`
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|-- `__snapshots__/View-test.tsx.snap.node`
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|-- `__snapshots__/View-test.tsx.snap.web`
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### Extensions
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To test specific platforms you can use the following extensions:
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- iOS: `-test.ios.*`, `-test.native.*`
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- Android: `-test.android.*`, `-test.native.*`
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- web: `-test.web.*`
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- Node: `-test.node.*`, `-test.web.*`
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### Mixing runners
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If you don't want to use every runner you can always mix runners by using the `projects` field of your Jest config. This will only work with single-runner projects like `jest-expo/ios`, `jest-expo/android`, `jest-expo/web`, and `jest-expo/node`.
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```diff
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"jest": {
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- "preset": "jest-expo/universal"
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// Skip web and Node tests
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+ "projects": [
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+ { "preset": "jest-expo/ios" },
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+ { "preset": "jest-expo/android"}
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+ ]
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},
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```
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### Testing JSX Components
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To test the output of your React components you can use the library **jest-expo-enzyme**, which extends `jest-expo` and adds universal [Enzyme](https://airbnb.io/enzyme/) support.
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### ⚙️ Configuring your preset
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When building a custom preset you may want to use some of features provided by this preset. You can access these features through the `jest-expo/config` directory.
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#### `getWatchPlugins(jestConfig)`
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When given an existing Jest config this will return the `watchPlugins` used in `jest-expo`. This reads the `projects` field to determine which watchPlugins to return for single-project and multi-project configs.
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Currently this returns type-ahead plugins for all projects:
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- `jest-watch-typeahead/filename`
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- `jest-watch-typeahead/testname`
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And a custom platform selection dialog for universal multi-projects:
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- `jest-watch-select-projects`
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#### `withWatchPlugins(jestConfig)`
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Given a Jest config, this will ensure any existing `watchPlugins` are safely merged with `getWatchPlugins(jestConfig)`.
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#### `getWebPreset()`
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Alternative to `jest-expo/web`. This runs in a JSDOM environment for testing **Expo web**.
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#### `getIOSPreset()`
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Alternative to `jest-expo/ios`. Runs in a mock native environment.
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#### `getAndroidPreset()`
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Alternative to `jest-expo/android`. Also runs in a mock native environment.
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#### `getNodePreset()`
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Alternative to `jest-expo/node`. This runs in a Node environment for testing **SSR**.
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### Learning Jest
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[Read the Jest documentation](https://facebook.github.io/jest/)
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