You are right on the nose!you have to be tested and licensed contact the texas dept arg. for test info. test cost nothing I believe and sale permit goes by number birds you have
This website talks about showing and selling legally: shows require a P/T test, and auctions require a sales license. If you have under 100 birds the license costs about $35
https://tvmdl.tamu.edu/wp-content/uploads/2012/08/Poultry-programs1.pdf
Testing for Pullorium-Typhoid Certificate is done through Texas A&M Veterinary Medical Diagnostic lab.
Then a different agency supplies the license, and to get the license you have to have an up-to-date P/T certificate. Texas Animal Health commission
http://www.tahc.state.tx.us/animal_health/poultry_registration.html
Technically poultry isn't even supposed to be moved without the correct paperwork...but it is mostly aimed at large commercial producers not us backyarders.
good luck with it.