How reliable are Ayurveda constitution tests?

Vata, Pitta or Kapha - which „Dosha type“ are you? Numerous online providers and print media attract interested parties with questions like these, using a questionnaire to identify health strengths and weaknesses, personality traits, inclinations and needs in just a few minutes. Is this even possible from a classical Ayurvedic point of view? How reliable are such constitution tests? And how can a layperson recognise professional tests [...]?