react-native-vision-camera/docs/docs/guides/MOCKING.mdx

---
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/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.