Its a mock of react-native AsyncStorage for jest tests

NPM

// jest.config.js
module.exports = {
  setupFilesAfterEnv: [
    '<rootDir>/setup-tests.js',
  ],
};

// setup-tests.js
import MockAsyncStorage from 'mock-async-storage';

const mockImpl = new MockAsyncStorage();
jest.mock('@react-native-community/async-storage', () => mockImpl);

import MockAsyncStorage from 'mock-async-storage';
// or import { mock, release } from 'mock-async-storage';
// mock();
// release();

const mock = () => {
  const mockImpl = new MockAsyncStorage()
  jest.mock('AsyncStorage', () => mockImpl)
}

const release = () => jest.unmock('AsyncStorage')

mock();

// For unmock
mockStorage.release();

Working example:

import 'react-native';
import MockAsyncStorage from 'mock-async-storage'
import React from 'react';
import Index from '../index.android.js';

// Note: test renderer must be required after react-native.
import renderer from 'react-test-renderer';

const mock = () => {
  const mockImpl = new MockAsyncStorage()
  jest.mock('AsyncStorage', () => mockImpl)
}

mock();

import { AsyncStorage as storage } from 'react-native'

it('renders correctly', () => {
  const tree = renderer.create(
    <Index />
  );
});

it('Mock Async Storage working', async () => {
  await storage.setItem('myKey', 'myValue')
  const value = await storage.getItem('myKey')
  expect(value).toBe('myValue')
})

In your test codes:

const mockStorage = require('mock-async-storage');
// or import { mock, release } from 'mock-async-storage';
// mock();
// release();

// For mock AsyncStorage
mockStorage.mock();

// For unmock
mockStorage.release();

Working example:

import 'react-native';
import { mock, release } from 'mock-async-storage'
import React from 'react';
import Index from '../index.android.js';

// Note: test renderer must be required after react-native.
import renderer from 'react-test-renderer';

mock()

import { AsyncStorage as storage } from 'react-native'

it('renders correctly', () => {
  const tree = renderer.create(
    <Index />
  );
});

it('Mock Async Storage working', async () => {
  await storage.setItem('myKey', 'myValue')
  const value = await storage.getItem('myKey')
  expect(value).toBe('myValue')
})