Writing tests documentation

so this is partially a question, but since the docs are lacking a bit, what is the right way to replace a singleton for a test? my initial thought was to create a child container for the mocks, but it turns out that only works with explicit calls to resolve, it doesn't work if trying to replace a singleton.

So I have this class, it takes an OrderService

@singleton()
export default class OrderCompleteHandler implements Handler<OrderEventType,any> {
  constructor(
    @inject(InjectToken.Logger) private readonly log: Logger,
    private readonly svc: OrderService) {
  }

  async handle(queue: OrderEventType, msg: ConsumeMessage): Promise<any> {
    const json = JSON.parse(msg.content.toString('utf8'));
    this.log.debug(json);
    return await this.svc.onDrinkIsComplete(json as DrinkComplete);
  }

}

@singleton()
export default class OrderService {

now I want to replace order service with my own implementation, in my test, and only in that test

what I've come up with is this

test('order complete de-serialization', async (done) => {
  rootContainer().register(OrderService, { // rootContainer() is a simple method call for container
    useFactory: instanceCachingFactory((c) => {
      return {
        async onDrinkIsComplete(drink: DrinkComplete): Promise<void> {
          done();
          return;
        }
      };
    })
  });
  const container = (await testContext).testContainer();
  const sender = container.resolve(AmqpSender);
  const msg: DrinkComplete = {
    id: 1234,
  };
  await sender.send(Amqp.OrderExchange, OrderEventType.DrinkComplete, msg);
});

but that feels like it will replace it completely in the context for all test runs... or rather just add another instance, is this the right way? or is there a better way? can I unregister just this dependency? is there a way to make the child container resolve first instead of the singleton?