> For the complete documentation index, see [llms.txt](https://docs.nestjstools.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.nestjstools.com/clock/getting-started/usage-example.md).

# Usage example

### Injecting the Clock

```
import { Injectable } from '@nestjs/common';
import { IClock, Clock } from '@nestjstools/clock';

@Injectable()
export class SubscriptionService {
  constructor(@Clock() private readonly clock: IClock) {}

  isSubscriptionActive(startDate: Date, durationDays: number): boolean {
    const now = this.clock.now();

    const endDate = new Date(startDate);
    endDate.setDate(endDate.getDate() + durationDays);

    return now < endDate;
  }
}
```

Notice:

* No `new Date()` inside domain logic
* Time is injected
* Fully testable

***

## 🧪 Testing

Override the clock in tests:

```
import { Test } from '@nestjs/testing';
import { SubscriptionService } from './subscription.service';
import { FixedClock, Service } from '@nestjstools/clock';

describe('SubscriptionService', () => {
  let service: SubscriptionService;

  beforeEach(async () => {
    const moduleRef = await Test.createTestingModule({
      providers: [SubscriptionService],
    })
      .overrideProvider(Service.CLOCK_SERVICE)
      .useValue(new FixedClock(new Date('2020-10-10T00:00:00Z')))
      .compile();

    service = moduleRef.get(SubscriptionService);
  });

  it('returns true when subscription is active', () => {
    const start = new Date('2020-10-01T00:00:00Z');
    const active = service.isSubscriptionActive(start, 20);

    expect(active).toBe(true);
  });

  it('returns false when subscription expired', () => {
    const start = new Date('2020-09-01T00:00:00Z');
    const active = service.isSubscriptionActive(start, 20);

    expect(active).toBe(false);
  });
});
```

Deterministic. Predictable. Clean.


---

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