...It distinguishes between different kinds of tests—unit, integration, end-to-end—and shows when each is appropriate given time and risk constraints. The guide focuses on removing flakiness by isolating side effects, controlling randomness, and stabilizing async code paths. It also demonstrates test design techniques like arranging test data, using expressive assertions, and structuring test suites for readability and discoverability. Tooling agnosticism is a theme: patterns are illustrated with popular tools but written to survive framework churn. The end goal is a test suite that acts as living documentation while catching regressions quickly and deterministically.