Wrote ScorePackageManager tests. MILESTONE.

MILESTONE: Test files now exist for all 41 ScorePackageaManager public methods.
ScorePackageManager public methods and ScorePackageManager commands are all now
implemented 1:1.

MILESTONE: MaterialPackageManager, SegmentPackageManager, ScorePackageManager
are all now tested. All three package manager classes are now tested.

The seven concrete wrangler classes will follow.