FIxed bugs in the simulation core unit test. It now uses more realistic,
arithmatic-resiliant (read: slow) methods for figuring out whether or
not it should continue simulting. Additionally, I modified the test to use
positive and negative values for x/y. No additional bugs outside of the test
needed to be fixed, amusingly enough.

Signed-off-by: null <gorha032@umn.edu>