A person has diabetes 1 and doctor has opposed fasting for him due to unstable sugar levels. The person needs to inject insulin 4 times everyday. The person feels that he may keep 1 or 2 roza, which is around 17+ hrs fasting (Denmark), so is it allowed to try and test if he can keep fasts when the doctor is against fasting?

If the person believes that trying to fast 1 or 2 days is not harmful to his health, then yes he is allowed to try even if his doctor advises him not to. But if he believes that trying to fast a day or two will harm him, then he should not. As long as he doesn’t believe he will be harmed, then he can try fasting.