Another way to test is by using the training dummies. There is an unarmored one on the ground, but two armored ones up on a balcony near the back left (outer wall). You can test weapons on them, to see how they do against armor. Some weapons may damage armor but still do very little damage, so this is a great way to test it. You can be sure a weapon doesn’t penetrate armor if you hit and it says zero. At power 600, it seems that numbers in the 2000-3000 range are good. Chaos Warriors on Legend have around 120,000 health (by the scale used on test dummies), so being able to kill them in as few blows as possible is great.
Bear in mind; not all attacks currently register on the dummies, so if you attack and don’t see any numbers, it doesn’t mean it does no damage, but that the dummy doesn’t register it yet. This is because the dummies were added (by suggestion? not sure) late in development and had to be specially coded due to the Keep not functioning like a regular map.