Expand Test Coverage

[gunnarmiller]

Currently the testing suite for the repo covers many of the key classes and methods, but far from all. Classes that need the most attention are

1. Miner
2. TrialManager
3. SpiralPlotter
4. ScoreTreeBranch
5. ProofOfWorkProtocol

These are all complicated classes with many things that can go wrong that currently have no direct test coverage. Test coverage for some other classes could also stand to be improved, especially BlockScoreTree, which is very easy to unwittingly break when modifying it.