How to design psychology tests for concept formation?
There's no one good answer to this unfortunately, the question is too broad. Seems like you have made a decent start, here are two more quite different methods-focused references to add to your reading that might help:

Divjak, Dagmar, and Antti Arppe. "Extracting prototypes from exemplars What can corpus data tell us about concept representation?." (2013): 221-274.

Lee, Michael D., and Wolf Vanpaemel. "Exemplars, prototypes, similarities, and rules in category representation: An example of hierarchical Bayesian analysis." Cognitive Science 32.8 (2008): 1403-1424.