---id: testingtype: guideowner: justindescribes:  - test/helpers/**reviewed: 2026-10-01---# Running and writing tests```bashnpm test          # node --test over test/**/*.test.tsnpm run typecheck```The tests need only Node 24. They do not start workerd or wrangler.## How it works`test/helpers/app.ts` builds the real fetch handler from `createApp` with a fresh environment per test:- `DB` is `TestD1` (`test/helpers/d1.ts`), a small D1 stand-in over `node:sqlite` with every file in `migrations/` applied in order and foreign keys on. It covers `prepare`, `bind`, `first`, `all`, `run` and `batch`, and a batch is a transaction, as in D1.- `IMAGES` is `TestR2` (`test/helpers/r2.ts`), an in-memory bucket.- The clock is fixed and ids count up (`id-1`, `id-2`), so assertions can name them.Tests talk HTTP to the handler through `call(method, path, body, headers)`, which returns the status, headers and parsed JSON. `addProduct` creates a product with the admin token.## Writing oneTest behavior through the API rather than the modules, the way a client sees it. When code calls a D1 method the stand-in does not have yet, add it to `TestD1` in the same change. A new migration needs nothing: the stand-in applies whatever is in `migrations/`. See [[0001-d1-for-shop-data]] for why the SQL is shared.