For developing there is tons of information out there for many combinations of film and developer, often at multiple dilutions, temperatures and ISO settings. Ilford for example has development times for its various developers and films in their manuals, and even some films of other vendors. The Massive Dev Chart has an immense collection of combinations.
So how exactly are these established? Is there some procedure? Say, shooting a reference image at various ISO settings and then making measurements of highlights, shadows, contrast and grain? Or is it a much more subjective process where trial-and-error is applied and the end results interpreted by experienced people? Would a producer of film and/or developer such as Ilford or Kodak use different means than people contributing to the Massive Dev Chart?