More GoEngine tests

[benjaminpjones]

Raises GoEngine.ts test coverage from 67% to 77% (62% -> 64% globally)

Still missing a lot of edge cases, but at least this gets the happy path for a lot of GoEngine methods :)

Notes:

• the deleted file GoEngine_computeScore.test.ts was merged into the larger GoEngine.test.ts file.
• Also the commit messages aren't so precise on this one - let me know if I should just rebase. I figure commit granularity isn't so important this time since these are just tests, not production code.

[anoek]

Awesome, thanks for the tests!