A person's refusal to do anything that looks like a test can turn into a significant challenge. A childhood onset of a cognitive disability tends to produce bad experiences with tests. Doing an activity that does not look like a test is a big help. Do not say or think the word "test".
Taking a few minutes to talk a new person, when they can talk, is time well invested. A relaxed conversation often gains cooperation and provides better information than standardised interviews and self-reports.