Solving the Jest Native Module Error in a React Native Expo Project

While working on a React Native Expo project, I encountered a perplexing error message during my Jest tests. The error halted my progress and left me searching for a solution. Here's a detailed account of the error and how I resolved it

The error message I encountered was as follows:

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Cannot find native module 'ExpoClipboard'

   7 |   Box,
   8 | } from 'native-base'
>  9 | import * as Clipboard from 'expo-clipboard'
     | ^
  10 |
  11 | import { Job, JobStatus, Service, Photo } from '../../types/JobModel'
  12 | import { NativeStackNavigationProp } from '@react-navigation/native-stack'

  at Object.requireNativeModule (node_modules/expo-modules-core/src/requireNativeModule.ts:17:11)
  at requireNativeModule (node_modules/jest-expo/src/preset/setup.js:257:73)
  at Object.<anonymous> (node_modules/expo-clipboard/src/ExpoClipboard.ts:3:35)
  at Object.<anonymous> (node_modules/expo-clipboard/src/Clipboard.ts:11:1)
  at Object.<anonymous> (src/screens/JobEdit/index.tsx:9:1)
  at Object.<anonymous> (src/screens/JobEdit/index.test.tsx:4:1)

The error message clearly indicated that Jest was unable to find the native module ExpoClipboard. This issue arises because Jest tests run in a Node environment, which does not support native modules used in a React Native application.

After some research, I found a solution to mock the expo-clipboard module in the Jest environment. By mocking the module, I could bypass the need for the native environment and ensure my tests ran smoothly. Here’s the code that solved the issue:

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jest.mock('expo-clipboard', () => ({
  getStringAsync: jest.fn(),
  setString: jest.fn(),
}));

This snippet creates a mock version of the expo-clipboard module, providing mock functions for getStringAsync and setString. This mock setup ensures that any calls to these functions within the tests will use the mocked versions instead of attempting to access the real native module.

To apply this solution, you need to add the mocking code to your Jest setup file. If you don't have a Jest setup file, you can create one, typically named jestSetupFile.js. Here's how to include the mock:

1. Create or open your Jest setup file (e.g., jestSetupFile.js).

2. Add the mock code to the file:

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   jest.mock('expo-clipboard', () => ({
     getStringAsync: jest.fn(),
     setString: jest.fn(),
   }));

3. Ensure that your Jest configuration is set to use this setup file. You can do this in your jest.config.js or package.json under the Jest configuration section:

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   "jest": {
     "setupFiles": ["<rootDir>/jestSetupFile.js"]
   }

With the mock in place, you can now run your tests again. The error should be resolved, and Jest will use the mocked functions instead of trying to access the native ExpoClipboard module.

Encountering issues like the native module error in Jest can be frustratin. By mocking the expo-clipboard module, I was able to run my tests without errors, allowing me to continue developing my React Native Expo project smoothly.

If you encounter similar issues with other native modules, consider mocking them in the Jest environment using the same approach. Happy testing!