Fix unorganized test structure

[Ethan Arrowood]

I was reviewing this repo recently and noticed the unit-tests are unorganized. There is a root level types.test.ts file and then within the tests/ directory there are normal .js and .ts files. I'm going to take a stab at cleaning this up and additionally expose any missing typings or what not.

[Maksim Sinik]

This issue was resolved by 63 and others.