Best test for a runner with ankle sprain

If you're out on a run and you roll your ankle, you need to know how you can test the ankle to figure out what is wrong.
 
More importantly, what tests can tell you how likely it is that you're actually going to get back to running and not have an ankle sprain again.  

There are several tests doctors use in evaluating injured ankles. Some are more important than others.

What is the single most important test for a runner with an ankle sprain? 
 
Well, that's what we're talking about today on the Doc On The Run Podcast.