Implement a limited number of high priority unit tests

[jackbaker1001]

There are presently no unit tests at all in the repo. It is very likely that we will not have time to achieve high test coverage, but we should identify some key areas to test.

As I progress through understanding the code base internals, it will become more obvious which parts these are and we can discuss below.

[PabloAMC]

We may want to close this, or are there additional tests to be implemented?

[jackbaker1001]

I think I will add some basic unit testing for Molecule and Functional classes. I think Integration testing is as good as it needs to be though!