We are trying to do the food allergy test on my 6 month old but he won't eat any of the vegetables we've tried. What do I do?

Plan B. There are various ways to get information on food alllergies for your child. Bloodwork can provide suggestion of food allerrgies. Skin tests, though uncomfortable, provide added info. The food challange is by far the most reliable of the three but requires babies cooperation. I generally don't food test kids this young unless they have eczema, chronic nasal drainage & infections etc.
Keep trying. A 6 month old really does not know what they like and dislike. Some children do not take to certain foods, while others seem to take to all of them. One technique is to give the child the same food for a week. In particular, try the vegetables first, and avoid the fruits, as they are much sweeter.