public async Task given_already_existing_attendable_event_new_one_should_not_be_added()
        {
            var attendableEvent = GetAttendableEvent();
            var @event          = new AgendaItemAssignedToAgendaSlot(Guid.NewGuid(), attendableEvent.Id);

            _attendableEventsRepository.GetAsync(@event.AgendaItemId).Returns(attendableEvent);

            await Act(@event);

            await _attendableEventsRepository.Received(1).GetAsync(@event.AgendaItemId);

            await _agendasApiClient.DidNotReceiveWithAnyArgs().GetRegularAgendaSlotAsync(default);
 private Task Act(AgendaItemAssignedToAgendaSlot @event) => _handler.HandleAsync(@event);