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);
}