I've seen videos where guys will film the action of a fly in a fishtank with an adjustable circulator or something to create current at different speeds to test action of a pattern. Lot of tyers will just use a GoPro on the water and shoot footage below the surface.
My waters are normally pretty clear, so I just cast along the bank and wear polarized glasses and change up my retrieve to see if whatever I made is moving well or it's a dud. Articulated shanks have really changed how much movement I can get, and I find myself tying more of those than anything, even if it only has 2-3 shanks along with the hook. Running a bunch of small ones that increase a bit in length, more material for a nice taper, and they move surprisingly like a fish. Just have to make sure they stay keeled.