Here’s a long article describing what to be careful of when tying into an anchor based on the results of these tests.
Don’t leave slack in your sling when you’re attached to a belay anchor. Use the climbing rope if you can. An 11mm Dyneema sling will break with a two foot fall if it has a knot in it.
Once curious point in the video is that tying an overhand knot in a nylon sling, reduces the force.