Jest - HelpMeTest (Page 2)

Testing

Testing Feature Flags with Flagsmith and Jest: Targeting Rules and Local Evaluation

Flagsmith supports local evaluation mode where flag rules are downloaded once and evaluated in-process. This makes it ideal for testing—no HTTP calls during test runs. This guide covers testing flag evaluation, targeting rules, percentage rollouts, and identity overrides in Jest without a running Flagsmith instance. Why Flagsmith Is

Prisma

Testing Prisma ORM: Unit Tests with Mocking and Integration Tests with TestContainers

This post covers two complementary strategies for testing Prisma ORM: fast unit tests using jest.mock to stub @prisma/client, and reliable integration tests using TestContainers to spin up a real Postgres instance. You'll learn how to keep your test suite both fast and trustworthy by knowing when

Expo

Testing Expo Apps: Jest Unit Tests, Expo Router Testing, and E2E with Detox

Expo adds a layer of abstraction over React Native that requires specific testing strategies. The jest-expo preset handles most of the configuration complexity, but mocking expo-* modules, testing Expo Router's file-based navigation, and connecting Detox to the bare workflow each have their own patterns. This guide

Apollo Server

Testing Apollo Server: Resolvers, DataSources, and Subscriptions with Jest

Apollo Server v4 introduced a cleaner testing API centered on executeOperation, which lets you run full GraphQL operations without spinning up an HTTP server. This post covers testing resolvers, DataSources, authentication via context, subscriptions with graphql-ws, and how to use snapshot testing effectively for GraphQL responses — all with Jest.

React Native

React Native Testing Library: Component Tests, Native Module Mocks, and Async Utils

@testing-library/react-native brings the same user-centric testing philosophy to mobile that Testing Library brought to the web. This guide covers component rendering, custom hook testing with renderHook, mocking stubborn native modules, taming async state with waitFor and findBy, and the act() gotchas that trip up even experienced

Testing

Socket.io Testing: Unit Tests with Jest, Integration with Supertest

Socket.io applications require testing at three layers: the HTTP upgrade handshake, the event protocol layer (emit/on, ACKs, rooms), and real concurrency behavior under load. This guide covers in-process test setup, Jest event testing, middleware mocking, and scalable load patterns. Socket.io is the de-facto standard for

Testing

Jest Snapshot Testing: Complete Guide to Writing Reliable Snapshots

Jest snapshot testing is simultaneously the most misused testing feature in the React ecosystem and genuinely useful when applied correctly. Teams either avoid it entirely (too fragile) or over-use it (snapshot everything and update blindly). Neither is right. This guide covers how snapshot testing actually works, when it provides