ConcurrencyException reports an incorrect expected revision number.

[ElasticCoder]

The InMemoryStorageEngine reports an incorrect expected revision number. It is off by 1.

if (firstEvent.EventNumber - 1 != streams[streamId].Count)
{
    throw new ConcurrencyException($"Concurrency conflict when appending to stream {streamId}. Expected revision {firstEvent.EventNumber} : Actual revision {streams[streamId].Count}");
}

It shoud read:

if (firstEvent.EventNumber != streams[streamId].Count + 1)
{
    throw new ConcurrencyException($"Concurrency conflict when appending to stream {streamId}. Expected revision {firstEvent.EventNumber} : Actual revision {streams[streamId].Count + 1}");
}

SimpleEventStore/src/SimpleEventStore/SimpleEventStore/InMemory/InMemoryStorageEngine.cs

Line 29 in 60f1460

throw new ConcurrencyException($"Concurrency conflict when appending to stream {streamId}. Expected revision {firstEvent.EventNumber} : Actual revision {streams[streamId].Count}");