Start with the simple stuff

Well you have written a bunch of rules and most of them are non fatal if tested, so you start with the simple and "safe" stuff, and then you move down the list.

Objects are absorbed

Well I have a slight objection to that one: absorbed as in encased and kept indefinitely or dissolved and excreted?

Test: Push a sewing needle into your arm.

Success: Needle is gone after some amount of time.

Failure: Needle causes discomfort, infection, inflammation or otherwise hurt you.

Keeping safe from failure: Visit a doctor and have the needle extracted.

Cannot drown

Test: Jump into a pool at the shallow end and crouch down. Bring a buddy if you wish for extra safety.

Success: Still alive after 10 minutes with no ill effects.

Failure: Feeling the usual feelings of panic and discomfort of not being able to breathe. Starting to get grey-out and tunnel vision.

Keeping safe from failure: stand up and breathe.

Cannot get fat

Test: Eat excessively. Monitor your body temperature

Success: You do not get fat. Body temperature rises.

Failure: You gain weight.

Keeping safe from failure: Stop over-eating.

Fast healing 1

Test: injure yourself lightly. See how long it takes to heal and if that varies depending on how much you eat.

Success: wounds heal without scarring or discoloration, and they do so depending on your food intake.

Failure: scarring results. Wound do not heal any faster compared to what they would normally.

Keeping safe from failure: Stop injuring yourself

Fast healing 2

Test: Cut off some part of yourself, like a centimeter wide flap of skin, as if say removing a birthmark or a mole. That cannot heal on a normal person without scarring.

Success: The cut is healed without scarring.

Failure: The cut is not healed without scarring.

Keeping safe from failure: Sorry, you will have to put up with that scar.

Fast healing 3

Test: Donate blood five days days in a row. No normal person reacts well to losing five pints of blood in that short amount of time.

Success: You do not experience dizziness or other signs of low blood pressure.

Failure: You start to feel the symptoms of blood loss.

Keeping safe from failure: stop donating blood as soon as you feel the least bit ill.

Fast healing 4

Test: Cut off the tip of a finger

Success: the finger heals without trace of injury

Failure: the fingertip does not regenerate

Keeping safe from failure: again, sorry, it is gone... but a fingertip is easy to live without.

Fast healing 5

Test: Stab yourself in the lung

Success: you heal without sign of injury

Failure: you start experiencing great difficulty to breathe

Keeping safe from failure: call emergency services and have them patch you up at the hospital. Blame a mugging or something like that.

Fast healing 6

I think you get the idea by now...