I have gotten into the habit of saving all my film leaders (35mm) cut off before loading films onto the development reels and use them to test the activity of the developer.
I simply take 20-30ml of mixed dev in a saucer and place the film leader in and leave for a few mins while I load the reels. If it goes black then at least I know the dev is working.
This came about after getting a clear film when my Pyrocat-HD had past its prime. Now I hopefully wont run into clear negs again (for that reason anyway)
Is this a valid test? Anyone do something similar?