The ultimate test is the test we do every time we squat over a toilet bowl. The only question to ask is, are you digesting your food properly? There are other definite indicators such as hiccups, burping, acid reflux, "sore stomach" (liver), pain between the shoulder blades, difficult and tense breathing.
You can increase and stimulate bile production naturally with bitter herbs and certain foods but once again, if bile flow is occluded and blocked by stones then such a protocol is useless. I myself have done this in the past with unsuccessful Liver Flushing and dietary/herbal protocols...it wasn't until my first successful Liver Flush that i saw immediate and drastic improvements in my bile flow. Preparation is everything!