Advanced Testing — Series 2

Preview — 3 of 10 questions

What is the argument for form (2) despite its cost?

javascript

// (1) TypeOrmModule.forRoot({ type: 'sqlite', database: ':memory:', synchronize: true })
// (2) a PostgreSQL container started for the test run

ASQLite cannot be used with TypeORM at all

BContainers start faster than an in-memory database

CSQLite's dialect differs from PostgreSQL in ways that matter — JSONB, arrays, ILIKE, partial indexes, ON CONFLICT behaviour, transaction isolation, even type coercion — so tests can pass against SQLite while the same query fails or behaves differently in production; testing against the real engine removes that whole class of false confidence

DIn-memory databases lose data between tests, making assertions impossible

How should this be tested?

javascript

@Injectable()
export class ReportJob {
  @Cron('0 3 * * *')
  async run() { await this.reports.generateDaily(); }
}

ATest run() directly as an ordinary method for its behaviour, and — if the schedule itself matters — assert on it separately through SchedulerRegistry, rather than trying to make the test wait for a cron tick

BUse jest.setTimeout(86_400_000) and let the schedule fire naturally

CTemporarily change the expression to * * * * * * in the test so it fires every second

DScheduled jobs cannot be tested and should be verified manually in staging

How is this tested without a seven-second test?

javascript

async fetchWithRetry(url: string) {
  for (let i = 0; i < 3; i++) {
    try { return await this.http.get(url); }
    catch { await sleep(2 ** i * 1000); }
  }
  throw new ServiceUnavailableException();
}

AMock fetchWithRetry itself and assert it was called

BReduce the real delays to one millisecond in a test-only configuration branch

CAccept the runtime; retry logic is inherently slow to verify

DInject the delay mechanism — a clock or sleep function — and substitute one that resolves immediately, or use jest.useFakeTimers() and advance them; the test then asserts the number of attempts and the backoff values requested, without any real elapsed time

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