Unit testing with Jest
We write thorough Jest tests across every TypeScript project: unit tests, integration, mocks, snapshots. A codebase that holds up over time.
What is Jest JavaScript testing?
Jest is the most widely used JavaScript unit testing framework. It works with TypeScript, React, Node.js and NestJS without complex configuration. Its built-in mocking system, native code coverage and parallelization make it the go-to tool for keeping quality high over the long run.
Why we test with Jest
Powerful mocks
Modules, functions, timers, fetch: Jest mocks everything without external dependencies. Unit tests stay isolated and fast.
Native coverage
A readable coverage report on every run. You know exactly which lines aren't covered by tests.
Snapshots
React render tests with snapshots: we catch visual regressions before they ever reach production.
Parallelization
Jest runs unit tests across parallel workers. Thousands of tests in seconds on CI.
What Jest changes for your codebase
Fewer regressions, confident refactors: a unit test suite that protects your investment.
Regressions caught early
A Jest test that breaks on CI costs you 10 minutes. A bug in production costs you hours and your users' trust.
Refactor with confidence
Solid Jest unit test coverage lets you rewrite code without fear of breaking something invisible.
Living documentation
Jest tests describe how your code is meant to behave. The best documentation is the one that fails when the code drifts.
Faster onboarding
A new developer understands the interface contracts just by reading the unit tests.
Our Jest discipline, in numbers
What we test with Jest
We combine Jest with
The stack that surrounds Jest on our projects.
How we set up Jest
Every stack comes with its own ecosystem. We always pick the technologies best suited to your project, based on its needs and its context.
To get started with Jest JavaScript testing on an existing project: install jest and ts-jest, configure jest.config.ts with coverage thresholds, then write your first unit tests on the critical business logic. We handle this setup end to end.
Vitest is faster with Vite because it shares the same config. Jest is more mature with broader compatibility. We use Jest for unit tests on Node/NestJS projects and Vitest on Vite/React projects.
Yes, with React Testing Library. We test user behavior (clicks, forms, navigation) rather than implementation details.
We use Jest mocks for the repositories, or spin up a test database in Docker for integration tests.
No. Coverage measures the lines executed, not the cases tested. We complement Jest unit tests with Playwright for E2E testing.
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A codebase tested with Jest
We put a rigorous Jest test suite in place on your project. Coverage, mocks, CI: quality that lasts.
Test my project with Jest