tests/ sits beside src/ so the source tree contains source and nothing else. The split is by cost, which is what makes it useful — you can run the cheap ones on every save and the expensive ones on demand.

pnpm test              # units + integration
pnpm test:unit         # just units
pnpm test:integration  # just integration
pnpm e2e               # Playwright

e2e/ is excluded from Vitest explicitly. Vitest's default include matches *.spec.ts, and picking up Playwright specs fails with a confusing "two different versions of @playwright/test".

Outside CI the suite runs with three workers and a 15-second test limit (vite.config.ts). CI keeps vitest's defaults, so a test that is too slow still fails there. Pass --maxWorkers=<n> to use more workers on an idle machine.

Ask what it would take to make it fail for a reason unrelated to the thing it tests. If the answer is "a slow disk" or "a flaky browser", it is not a unit test.

• Stubs fetch, reads a file, parses the contract → units
• Renders a component that fetches → integration
• Drives a browser → e2e

@/… is src/, @tests/… is tests/. Tests import production code through @/ like anything else; there are no deep relative paths between the two trees.

support/contractResponse.ts validates every MSW fixture against api/openapi.yaml with ajv before returning it. A hand-written mock is a second, unversioned implementation of the API: without this, someone adds a field to the contract, the handler keeps returning the old shape, and component tests stay green about a payload production will never send. A drifted mock fails at the mock rather than inside whatever it was meant to be testing.

units/contract/ asserts structural invariants of the contract itself — the §13.5 student-payload boundary, the §6.5 public-endpoint rules, pagination, operationId uniqueness. Its helpers are unit-tested against synthetic documents, because a checker nobody checks is decoration.

units/styles/tailwind-classes.test.ts reads every colour utility (bg-, text-, border- and its side forms, ring-, shadow- and the rest) in src/ and fails when one names no --color-* or --shadow-* key of index.css's @theme, no Tailwind default and no non-colour utility. Tailwind generates no CSS for such a class, and a test that only asserts the class name passes anyway; bg-accent-soft shipped that way.

The scan is a token regex over each file's text with its comments removed, not a parse, so it sees a class the same way inside a template literal, cn(...), cva(...) and clsx(...), and it cannot tell a class from a string that looks like one. Variants, the /50 opacity suffix and the ! marker are stripped first. A value in brackets or parentheses (text-[13px], bg-(--x)) is arbitrary and skipped. The longest prefix wins, so border-t-brand is read as side border-t with colour brand, not as border with t-brand. A new non-colour suffix (say border-spacing-*) goes in the test's NON_COLOUR table, and a CSS word that merely starts with a prefix (border-box) in CSS_WORDS.

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