Code needs unit tests

[BartMassey]

Testing for GUI code with randomization is hard, but some basic unit tests for the other functions would give more confidence that all is well. See issue #10 for where some doctests might come from.

[KappaDistributive]

There are unit tests for the actual merging/shifting algorithm in the cli branch that I didn't move over when I implemented the GUI. Just moving those over and expanding them would be a good start.