Vitest

Repository configuration, projects, setup, imports/globals, environments, aliases, test placement, and cleanup own the test contract. Inspect them and nearby tests before adding generic patterns. Do not add globals, jsdom, coverage, new setup, or browser mode by default.

Workflow

Define the behavior or regression, test its observable public result, and mock system boundaries rather than the behavior under test. Follow local fixture and cleanup ownership. In Effect repositories, use established @effect/vitest conventions such as it.effect, Layers, and TestClock rather than generic replacements. For a bug fix, reproduce the failure before relying on a passing result when practical.

Read patterns for component, async, fixture, snapshot, tag, or browser questions; mocking for module, timer, spy, or global boundaries; configuration for projects, migration, coverage, or reporter selection; and troubleshooting for hangs, discovery, resolution, or flaky state.