public async Task SavingNewAggregateWithoutChangesHasNoSideEffects()
        {
            // arrange
            var eventStore = CreateEventStoreMock();
            var repository = new AggregateRepository <Counter>(eventStore.Object);
            var aggregate  = factory.CreateNew(Guid.NewGuid().ToString());

            // act
            await repository.Save(aggregate);

            // assert
            eventStore.Verify(e =>
                              e.Append(It.IsAny <string>(), It.IsAny <int>(), It.IsAny <IEnumerable <IAggregateEvent> >()),
                              Times.Never);
        }