Oops. It's hard to remember who knows what, and how much explanation to put in.
If you need to find out, put each rooster with a group of hens and hatch some eggs. Then check the feathering speed of the daughters. If any daughters are fast feathering, then their father carries fast feathering. If all daughters are slow feathering, they father is probably pure for slow feathering.
If the hens for the test are slow feathering, then all the sons will be slow feathering too. But if you use fast feathering hens for the test, and any sons feather quickly, that will also show that the rooster being tested has the fast feathering gene.