The testing itself is pretty simple. Poke the bird, get blood in the loop, and mix with the P/T antigen. If the mix is all lumpy and separated bird needs to be checked again for Pullorium Typhoid. If the mix mixes well and does not separate bird is clear. P/T is really not that common anymore, but can devastate flocks.
In regards to Pullorium Typhoid here is a link to explain it some.