remove describe.only in unit/model-test.ts and fix failing tests?

[fmquaglia]

See this line in mode-test.ts

It's making run just one test. git blame says it was added in 1cc5ca2ef92df273526ba36f47e318db1a420791 by @richmolj 12-21-2017.
Possibly a cruft left over from local testing efforts?

Pushed a PR