And I would like to know the tests for lactose intolerance?

Breath test. Lactose intolerance can be diagnosed by a lactose breath test. Check with you doctor on setting it up for you. However many times people know they are lactose intolerant because they have symptoms with milk products. If you stop lactose for 2 weeks and feel better, that is another way to diagnose it. See a dietitian for advice especially about calcium and vit d if avoiding dairy.