testing

Testing (Vitest + Testing Library + in-process DB)

Priority order — spend effort where bugs live

1. Services — business logic + DB access. Highest value.
2. Zod schemas — boundary validation edge cases.
3. Pure helpers in lib/.
4. Components — the four states (loading/error/empty/populated) and user interactions. Test through the DOM, not implementation.
5. Skip: trivial pass-through code, styles, Next.js framework behavior.

Service tests with a real (in-process) database

Test real query behavior, constraints, and indexes without mocking the ORM.

Postgres (default) — PGlite, an in-process Postgres:

import { PGlite } from '@electric-sql/pglite'
import { drizzle } from 'drizzle-orm/pglite'
import { migrate } from 'drizzle-orm/pglite/migrator'
import * as schema from '@/lib/db/schema'

const client = new PGlite()
export const testDb = drizzle(client, { schema })

beforeAll(async () => {
  // apply the committed migrations (or push the schema) to the fresh instance
  await migrate(testDb, { migrationsFolder: './drizzle' })
})
afterEach(async () => {
  // truncate all tables between tests
})

Put this in a shared src/test/setup-db.ts and stub @/lib/db with the test instance via vi.mock so services under test hit PGlite.

Mongo — mongodb-memory-server:

import { MongoMemoryServer } from 'mongodb-memory-server'
import mongoose from 'mongoose'

let mongod: MongoMemoryServer

beforeAll(async () => {
  mongod = await MongoMemoryServer.create()
  await mongoose.connect(mongod.getUri())
})
afterEach(async () => {
  await mongoose.connection.db?.dropDatabase()
})
afterAll(async () => {
  await mongoose.disconnect()
  await mongod.stop()
})

Stub dbConnect to a no-op in tests (connection is already open).

Conventions

• Test files: <name>.test.ts(x) next to the code under test.
• Names describe behavior: it('returns 409 result when email already exists').
• Arrange with real service calls or direct model inserts — no fixture dumps that hide what matters to the test.
• Every bug fix ships with a regression test that fails without the fix.
• Assert on outcomes (returned DTO, DB state, rendered text), not on spies, unless the call itself is the contract (e.g. revalidatePath was invoked).