I don't know who to test IDS exactly, but one thing you can do it, run a torrent client in your network.
If IDS is working Endian should report something like this in it's log(IDS)
snort[4389]: [1:2000334:9] ET P2P BitTorrent peer sync [Classification: Potential Corporate Privacy Violation] [Priority: 1]: {TCP} 5.5.5.5:51439 -> 5.5.5.5:17445
ps: The IP in this example are change just to save my a$$.