If you're selling seed, the Iowa Seed Law requires you to test. But a seed test is good business too for the farmer planting home-grown seed. Here's information on tests and costs and on sampling and mailing instructions.
Everson, L. E.
"Test Your Seed Before You Plant or Sell,"
Iowa Farm Science: Vol. 18
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol18/iss6/2