If it's just failure type we can use compound failure type in this situation. To your example it can be "checkstyle+unittest". And error message can be compound too.
Cedric (currently) has three fields he wants to record for each failure. Personally, I think this is a bit too much to try to squeeze into a single Build sensor data record. I suspect that putting each failure into its own Build sensor data entry will make processing easier and the representation easier to understand.
Cheers, Philip
