Mock Service Worker vs Testcontainers

Free and open source

Free tier available

Free and open source. You pay in engineering time and CI minutes.

Free. Testcontainers Cloud, which offloads container execution, is a paid Docker product.

Everything, self-hosted

The libraries are free and open source.

Category standard

OSS community · since 2020

Category standard

AtomicJar (Docker) · since 2015

• One set of handlers reused across unit, component, E2E and local development.
• Application code is completely unaware it is being mocked — no test-only branches.
• Supports REST and GraphQL with the same model.

• Tests run against the real database engine, so dialect and behaviour differences surface early.
• Containers are disposable, which removes shared-state flakiness entirely.
• Excellent language coverage with idiomatic APIs.

• JavaScript ecosystem only.
• Service Worker registration adds a setup step and occasional caching confusion.
• Handlers can drift from the real API without contract verification.

• Requires a Docker daemon in CI, which not every environment provides.
• Container startup adds seconds to each test run unless reused carefully.
• Heavier resource usage than in-memory alternatives.

Front-end teams that want one mocking approach across every kind of test.

Integration tests that currently use in-memory databases and lie to you.