more tests for pwdSimulator (wrt basals)

Sorta WIP. (In other words: the simulator is still marinating in my brain, and I may think of more and/or reconsider these tests.)

First two tests I added might be more for points of discussion, but I believe the third (re: settings change during a run of scheduled basals), which currently fails, poses more of a problem.

Whenever you're ready to discuss @cheddar @kentquirk