Jest-integration.md

Jest integration

Async Storage module is tighly coupled with its NativeModule part - it needs a running React Native application to work properly. In order to use it in tests, you have to provide its separate implementation. Follow those steps to add a mocked Async Storage module.

Using Async Storage mock

You can use one of two ways to provide mocked version of AsyncStorage:

With mocks directory

1. In your project root directory, create __mocks__/@react-native-community directory.
2. Inside that folder, create async-storage.js file.
3. Inside that file, export Async Storage mock.

export default from '@react-native-community/async-storage/jest/async-storage-mock'

With Jest setup file

1. In your Jest config (probably in package.json) add setup files location:

"jest": {
  "setupFiles": ["./path/to/jestSetupFile.js"]
}

2. Inside your setup file, set up Async Storage mocking:

import mockAsyncStorage from '@react-native-community/async-storage/jest/async-storage-mock';

jest.mock('@react-native-community/async-storage', () => mockAsyncStorage);

Testing with mock

Each public method available from Async Storage is a mock function, that you can test for certain condition, for example, if .getItem has been called with a specific arguments:

it('checks if Async Storage is used', async () => {
  await asyncOperationOnAsyncStorage();

  expect(AsyncStorage.getItem).toBeCalledWith('myKey');
})

Overriding Mock logic

You can override mock implementation, by replacing its inner functions:

// somewhere in your configuration files
import AsyncStorageMock from '@react-native-community/async-storage/jest/async-storage-mock';

AsyncStorageMock.multiGet = jest.fn(([keys], callback) => {
  // do something here to retrieve data
  callback([]);
})

export default AsyncStorageMock;

You can check its implementation to get more insight into methods signatures.

Troubleshooting

SyntaxError: Unexpected token export in async-storage/lib/index.js

Note: In React Native 0.60+, all @react-native-community packages are transformed by default.

You need to point Jest to transform this package. You can do so, by adding Async Storage path to transformIgnorePatterns setting in Jest's configuration.

"jest": {
  "transformIgnorePatterns": ["node_modules/(?!(@react-native-community/async-storage/lib))"]
}

Optionally, you can transform whole scope for react-native-community and react-native:

"jest": {
  "transformIgnorePatterns": ["node_modules/(?!(@react-native-community|react-native))"]
}