Both—we recommend testing all of your dogs, just in case
We recommend testing all dams and sires prior to breeding. Our lab can then develop a risk assessment for a litter of puppies from the test results of pairing a specific sire and dam. If one or both ends up as a carrier or at risk for a particular condition, we recommend testing the puppies as a portion of them could be at risk or carriers themselves.
The statistical chance of a litter containing carrier or at risk puppies can easily be calculated based on the parents' genotypes. That said, genetics sometimes can be a messy science. Because of that, we recommend that you test ALL of your dogs, litters included.