Guides & Learn

The concepts, practices, and patterns behind the playgrounds. Read a guide to understand the why, then jump into a playground to practice the how.

Fundamentals

The mental models that make every later decision easier.

beginner

What to Test (and What Not To)

A risk-based way to decide where tests pay off — and where they just slow you down.

6 min read

Practices

Day-to-day techniques for writing tests that earn their keep.

intermediate

TDD in Practice

Red-Green-Refactor as a design tool, not a ceremony — with the failure modes to avoid.

7 min read

intermediate

Designing Reliable E2E Tests

End-to-end tests catch what unit tests cannot — but only if you kill flakiness at the source.

8 min read

Patterns

Reusable structures for the recurring problems in test code.

intermediate

Mocking & Test Doubles

Stub, spy, mock, fake — five different tools that get lumped under one word. Know which to reach for.

7 min read

Prefer to learn by doing?

Every guide pairs with a hands-on playground where you can run the ideas in your browser — or grab a ready-made solution from the recipes.

Explore the playgrounds