LaunchDarkly Jest

Easily unit test LaunchDarkly feature flagged applications with jest

For more information, see the complete reference guide for unit testing.

Installation

yarn add -D @launchdarkly/jest

or

npm install @launchdarkly/jest --save-dev

Then in jest.config.js add @launchdarkly/jest/{framework} to setupFiles:

// jest.config.js
module.exports = {
  // for react-native
  setupFiles: ['@launchdarkly/jest/react-native'],
};

Usage

Use these 3 APIs for your test cases:

• mockFlags(flags: LDFlagSet): Mock flags at the start of each test case. Only mocks flags returned by the useFlags hook.

• getLDClient(): Returns a jest mock of the LDClient. All methods of this object are jest mocks.

• resetLDMocks(): Resets both mockFlags and getLDClient mocks.

Example

import React from 'react';
import { render, fireEvent } from '@testing-library/react-native';
import { mockFlags, resetLDMocks, getLDClient } from '@launchdarkly/jest/react-native';
import Welcome from './Welcome';

describe('Welcome component', () => {
  afterEach(() => {
    // reset before each test case
    resetLDMocks();
  });

  test('evaluates a boolean flag', () => {
    // arrange
    // You can use camelCase, kebab-case, or snake_case keys
    mockFlags({ 'my-boolean-flag': true });

    // act
    const { getByText } = render(<Welcome />);

    // assert
    expect(getByText('Flag value is true')).toBeTruthy();
  });

  test('captures a track call', () => {
    // arrange
    mockFlags({ myBooleanFlag: true });
    const client = getLDClient();

    // act
    const { getByTestId } = render(<Welcome />);
    fireEvent.press(getByTestId('track-button'));

    // assert: track gets called
    expect(client.track).toHaveBeenCalledWith('event-name', { foo: 'bar' });
    expect(client.track).toHaveBeenCalledTimes(1);
  });
});

Developing this package

# at js-core repo root
yarn && yarn build && cd packages/tooling/jest

# run tests
yarn test

Note

LaunchDarkly plans to support test data sources for the React Native and other client-side SDKs in the future. Once this feature is avaliable, we will deprecate this package.

Verifying SDK build provenance with the SLSA framework

LaunchDarkly uses the SLSA framework (Supply-chain Levels for Software Artifacts) to help developers make their supply chain more secure by ensuring the authenticity and build integrity of our published SDK packages. To learn more, see the provenance guide.

About LaunchDarkly

• LaunchDarkly is a continuous delivery platform that provides feature flags as a service and allows developers to iterate quickly and safely. We allow you to easily flag your features and manage them from the LaunchDarkly dashboard. With LaunchDarkly, you can:
  • Roll out a new feature to a subset of your users (like a group of users who opt-in to a beta tester group), gathering feedback and bug reports from real-world use cases.
  • Gradually roll out a feature to an increasing percentage of users, and track the effect that the feature has on key metrics (for instance, how likely is a user to complete a purchase if they have feature A versus feature B?).
  • Turn off a feature that you realize is causing performance problems in production, without needing to re-deploy, or even restart the application with a changed configuration file.
  • Grant access to certain features based on user attributes, like payment plan (eg: users on the ‘gold’ plan get access to more features than users in the ‘silver’ plan).
  • Disable parts of your application to facilitate maintenance, without taking everything offline.
• LaunchDarkly provides feature flag SDKs for a wide variety of languages and technologies. Read our documentation for a complete list.
• Explore LaunchDarkly
  • launchdarkly.com for more information
  • docs.launchdarkly.com for our documentation and SDK reference guides
  • apidocs.launchdarkly.com for our API documentation
  • blog.launchdarkly.com for the latest product updates