I’m not sure the kind of test you may have in mind; nevertheless, there are a variety of tests that could be administered to mentally challenged kids, all depends on your discretion. Your focus shouldn’t be the type of test to practice; the focus should be the probability that the lesson learned over time is truly grabbed. Some learn visually; in this case, tests may be administered pictorially or perhaps via reading/seeing.
Some are auditory learners; i.e., they most preferably learn by listening, tests, in this case, maybe administered verbally. Others are kinesthetic learners in a sense they learn by moving and doing things. The bottom line is that once you are sure of your teaching mechanisms, i.e., they understood properly what they are being taught either via auditory means, visual means or kinesthetics; you wouldn’t have to worry about the rightness or wrongness of a test to practice in as much it is in the confines of their syllabus.
The assessment for no refusals is to make sure that the person being assessed hasn’t already made a decision about a treatment when they were mentally able to do so. This is to make sure that, if so stated, they don’t go against a patient’s wishes to not receive a treatment.
Mental incompetency can be a major factor in why you would want to assess to make sure the patient hasn’t already said they wouldn’t like to receive a treatment. If they have a power of attorney for this point in their life, doctors should check with them to make sure they knew the patient’s wishes, or at least know where they might be able to find such wishes. If the patient has refused the treatment and wishes to continue to refuse it after they have been ruled mentally unable to make those decisions, those wishes should be honored.
When a person has capacity it means that they can absorb information and are able to make a decision whether you do or do not agree with them. It is within their ability to make a decision that is important and not just a decision that you would agree with.
This is the kind of person a leader would want as a participant, someone that can think for themselves and further whatever the cause might be in an intelligent thoughtful manner. The opposite would be a person that acts as though they are a zombie always agreeing just for the sake of agreeing and never thinking for themselves.