Add Unit Testing

[foster999]

It might be useful to implement unit testing for at least the key functions of the package. This would ensure that any future refactoring or development doesn't alter their function from that intended.

@SirBob01 if this seems like a good idea, would you have any preference of testing package (e.g. unittest or pytest)?

[SirBob01]

@foster999 I have no particular preference (I have this bad habit of only manually testing my code), but I'm more familiar with unittest.