react-native-vision-camera/docs/docs/guides/MOCKING.mdx
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---
id: mocking
title: Mocking
sidebar_label: Mocking
---
import useBaseUrl from '@docusaurus/useBaseUrl';
<div>
<img align="right" width="283" src={useBaseUrl("img/11_back.png")} />
</div>
The provided library doesn't work on simulators. These steps allow you to mock the library
and use it for developing or testing. Based on
[Detox Mock Guide](https://github.com/wix/Detox/blob/master/docs/Guide.Mocking.md).
### Configure the Metro bundler
In order to override React Native modules, allow bundler to use the flag `RN_SRC_EXT` to extend
`resolver.sourceExts`, and then prioritize any given source extension over the default one.
Add to your [Metro Config](https://facebook.github.io/metro/docs/configuration/):
```js
const { getDefaultConfig } = require("metro-config");
const { resolver: defaultResolver } = getDefaultConfig.getDefaultValues();
module.exports = {
...
resolver: {
...defaultResolver,
sourceExts: [
process.env.RN_SRC_EXT && process.env.RN_SRC_EXT.split(','),
...defaultResolver.sourceExts,
],
},
};
```
### Create proxy for original and mocked modules
1. Create a new folder `vision-camera` anywhere in your project.
2. Inside that folder, create `vision-camera.js` and `vision-camera.e2e.js`.
3. Inside `vision-camera.js`, export the original react native modules you need to mock, and
inside `vision-camera.e2e.js` export the mocked modules.
In this example, several functions of the modules `Camera` and `sortDevices` are mocked.
Define your mocks following the [original definitions](https://github.com/mrousavy/react-native-vision-camera/tree/main/package/src).
```js
// vision-camera.js
import { Camera, sortDevices } from 'react-native-vision-camera';
export const VisionCamera = Camera;
export const visionCameraSortDevices = sortDevices;
```
```js
// vision-camera.e2e.js
import React from 'react';
import RNFS, { writeFile } from 'react-native-fs';
console.log('[DETOX] Using mocked react-native-vision-camera');
export class VisionCamera extends React.PureComponent {
static async getAvailableCameraDevices() {
return (
[
{
position: 'back',
},
]
);
}
static async getCameraPermissionStatus() {
return 'granted';
}
static async requestCameraPermission() {
return 'granted';
}
async takePhoto() {
const writePath = `${RNFS.DocumentDirectoryPath}/simulated_camera_photo.png`;
const imageDataBase64 = 'some_large_base_64_encoded_simulated_camera_photo';
await writeFile(writePath, imageDataBase64, 'base64');
return { path: writePath };
}
render() {
return null;
}
}
export const visionCameraSortDevices = (_left, _right) => 1;
```
These mocked modules allows us to get granted camera permissions, get one back camera
available and take a fake photo, while the component doesn't render when instantiated.
### Use proxy module
Now that we have exported our native modules and our mocked modules from the same folder,
we must reference the proxy module.
```ts
// before
import { Camera } from 'react-native-vision-camera';
// now
import { VisionCamera } from '/your_path_to_created_folder/vision-camera/vision-camera';
```
### Trigger
Start Metro bundler with provided flag for using `.e2e.js` files.
Whenever Metro runs with `RN_SRC_EXT` environment variable set, it will override the default files with the ones set in `RN_SRC_EXT`.
```sh
RN_SRC_EXT=e2e.js react-native start
RN_SRC_EXT=e2e.js xcodebuild <params>
RN_SRC_EXT=e2e.js ./gradlew assembleRelease
```
On your simulator, with debug mode enabled, you should see
`"[DETOX] Using mocked react-native-vision-camera"`
## Issues
If testing doesn't work, try browsing the [GitHub issues](https://github.com/mrousavy/react-native-vision-camera/issues?q=is%3Aissue). If your issue doesn't exist, [create a new one](https://github.com/mrousavy/react-native-vision-camera/issues/new/choose). Make sure to fill out the template and include as many details as possible.