Testing

Tests live next to the code they cover — every *.spec.ts file sits in the same folder as its subject, and each service and lib runs its own Jest suite as an Nx target, so results are cached and only affected projects re-run.

npm test                          # all projects (Nx-cached)
npm run test:nocache              # same, ignoring the cache
npx nx run billing:test           # one service
cd backend/services/billing && npx jest src/path/to/file.spec.ts   # one file

The pre-commit hook runs the full suite (plus typecheck and lint), so a failing test blocks the commit.

Unit tests: no Nest, no mocks of your own code

Handlers are plain classes, so tests construct them directly — no Test.createTestingModule, no DI container, no framework boot. What varies is what you hand the constructor:

• In-memory repositories — every aggregate ships two repository implementations behind the same port. Tests use the in-memory one, which also takes a shouldFail flag so failure paths are one line to set up.
• Mock buses — MockCommandBus, MockQueryBus and MockEventBus from @libs/nestjs-common record what was dispatched (and can be told to fail), so a test asserts which command an event handler produced without executing it.

const repository = new Greeting_InMemoryRepository();
const eventBus = new MockEventBus();
const handler = new CreateGreeting_CommandHandler(repository, eventBus);
 
await handler.execute(new CreateGreeting_Command('Hello there', 'api'));
 
expect(await repository.findAll()).toHaveLength(1);
expect(eventBus.events[0]).toBeInstanceOf(GreetingCreated_DomainEvent);

The same style covers every handler type: command and query handlers get repositories and buses, domain-event handlers are usually self-contained, and integration-event handlers get a MockCommandBus to capture the command they translate the event into. A freshly generated service includes a working test of each kind.

Repository tests: one contract, every implementation

A repository's two implementations must behave identically — that's the whole point of the port. So the repositories aren't tested twice: a shared contract suite (exported from @libs/nestjs-common/test-exports) defines the behavior once, and each implementation runs it with its own setup:

describe('Outbox_MongodbRepository', () => {
  const mongoTestService = new MongodbTestService<OutboxEventDTO>(
    Outbox_MongodbRepository.CollectionName,
  );
 
  testOutboxRepositoryContract(
    'MongoDB Implementation',
    async () => new Outbox_MongodbRepository(mongoTestService.mongoClient),
    {
      beforeAll: () => mongoTestService.setupDatabase(),
      beforeEach: () => mongoTestService.clearCollection(),
      afterAll: () => mongoTestService.cleanup(),
    },
  );
});

The Mongo variants run against the real MongoDB from the dev stack — no in-process fake. jest.env.js sets NODE_ENV=test and clears MONGODB_URI, which routes connections to localhost:27017 (the dev compose exposes the port) and into a separate <service>-tests database, so tests never touch dev data. The practical consequence: repository tests need the dev stack running (npm run dev); pure unit tests don't.

Where the pieces come from

Aggregates and value objects also carry random() factories (Greeting.random(), Id.random(), …) so tests build valid domain objects in one call instead of hand-assembling props.