If you are testing using a non-specific test method (TOC or conductivity or pH), then you will likely test for the degredant at the same time, and be fairly accurate.
Even if using a specific test method (HPLC) In my experience we tested only for API (using HPLC) for 99% of the products. Remember, your allowable limits calculations has a safety factor built in (10, 100, 1000, etc.). This safey factor likely makes up for missing a few molecules of API which had degraded into something else.
Testing for degradants is a lot of additional work. What degredants are you looking for? What concentrations are expected, allowable, OK? I would 1st ask the question if you are expecting degredants in an appreciable manner? Also, would those degredants be adverse/toxic, or more toxic than the original API?
But, if you said yes that you expect a lot of degredants, then I wouldn’t see it passing stability testing at all. Maybe degredant testing would be needed for radiological products?
If your HPLC methods for finished product testing, can also be used for swab testing, then there is no reason to not look for degredants at the same time. But otherwise in the majority of cases degredant testing is probably not required during cleaning validation.