[Jest] _reactNativeMmkvStorage.MMKVLoader is not a constructor

[anhtuank7c]

Describe the bug Jest test failed when initializing an instance. Application working fine except jest scenario.

To Reproduce Steps to reproduce the behavior:

1. Integrate with Mobx state tree
2. initializing an instance in the model class
3. define a test scenario
4. See error

// Model class
import {Instance, SnapshotIn, SnapshotOut, types} from 'mobx-state-tree';
import {MMKVLoader} from 'react-native-mmkv-storage';

const devSettingStore = new MMKVLoader()
  .withEncryption()
  .withInstanceID('devSettings')
  .initialize();

/**
 * Model description here for TypeScript hints.
 */
export const FeatureFlagModel = types
  .model('FeatureFlag')
  .props({
    key: types.identifier,
    label: types.string,
    desc: types.optional(types.string, ''),
    selected: types.optional(
      types.union(types.union(types.string, types.undefined), types.null),
      undefined,
    ),
    defaultValue: types.string,
  })
  .views(self => ({
    get enabled() {
      return (self.selected || self.defaultValue) === 'enabled';
    },
    get defaultText() {
      return `Default (${self.defaultValue})`;
    },
  }))
  .views(self => ({
    get valueText() {
      return self.selected || self.defaultText;
    },
  }))
  .actions(self => ({
    loadCachedValue() {
      self.selected = devSettingStore.getString(self.key);
    },
    setValue(value: 'enabled' | 'disabled' | 'default' = 'default') {
      if (value === 'default') {
        self.selected = null;
        devSettingStore.removeItem(self.key);
        return;
      }
      devSettingStore.setString(self.key, value);
      self.selected = value;
    },
    reset() {
      self.selected = null;
      devSettingStore.removeItem(self.key);
    },
  }));

 // Jest test class
 import {FeatureFlagModel} from './feature-flag';

test('can be created', () => {
  const instance = FeatureFlagModel.create({
    key: 'test',
    label: 'Test',
    defaultValue: 'disabled',
  });

  expect(instance).toBeTruthy();
  expect(instance).toMatchSnapshot();
});

Expected behavior Jest test working good.

Screenshots

Platform Information:

System:
    OS: macOS 12.5.1
    CPU: (8) x64 Apple M1
    Memory: 26.59 MB / 16.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 18.7.0 - /usr/local/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v18.7.0/bin/yarn
    npm: 8.15.0 - ~/.nvm/versions/node/v18.7.0/bin/npm
    Watchman: 2022.07.04.00 - /opt/homebrew/bin/watchman
  Managers:
    CocoaPods: 1.11.3 - /Users/tuannguyen/.rvm/gems/ruby-2.7.5/bin/pod
  SDKs:
    iOS SDK:
      Platforms: DriverKit 21.4, iOS 15.5, macOS 12.3, tvOS 15.4, watchOS 8.5
    Android SDK:
      API Levels: 28, 29, 30, 31, 32, 33
      Build Tools: 28.0.3, 29.0.2, 30.0.2, 30.0.3, 31.0.0, 32.0.0, 32.1.0
      System Images: android-30 | Wear OS 3 - Preview ARM 64 v8a, android-32 | Google APIs ARM 64 v8a, android-33 | Google Play ARM 64 v8a
      Android NDK: Not Found
  IDEs:
    Android Studio: 2021.2 AI-212.5712.43.2112.8512546
    Xcode: 13.4.1/13F100 - /usr/bin/xcodebuild
  Languages:
    Java: 11.0.11 - /usr/bin/javac
  npmPackages:
    @react-native-community/cli: Not Found
    react: 18.0.0 => 18.0.0 
    react-native: 0.69.4 => 0.69.4 
   react-native-mmkv-storage: ^0.8.0
    react-native-macos: Not Found
  npmGlobalPackages:
    *react-native*: Not Found

I added an extra configuration to jest config.

https://rnmmkv.vercel.app/#/mockjest

[williamheelis]

I want to confirm: this is a major issue for us. Not sure what the cause is.

[williamheelis]

no jest unit test errors

import MMKVStorage from 'react-native-mmkv-storage';

const SecureStorage = new MMKVStorage.Loader()
    .withEncryption()
    .withInstanceId('someThing')
   .initialize();

hundreds of unit test errors

import { MMKVLoader } from 'react-native-mmkv-storage';

const SecureStorage = new MMKVLoader()
    .withEncryption()
    .withInstanceId('someThing')
   .initialize();