Well, they do have tests to test what breed is in a mixed dog or cat. Being het is generally a part of a mutation in the DNA and actually it is quite easy to test DNA no-a-days. I am not sure though if it is super important to actually test for hets or mutations in snakes for it to actually be done. DNA tests for dogs and cats were "invented" for professional dog and cat shows. To test DNA all they need is a tiny bit of blood but a test for dog breeds and snake color mutation would be different.