Fix type testing

When running tests with version 1.17.1 of mocha, I get this error on
several tests:

 Uncaught TypeError: Property 'a' of object #<Assertion> is not a
 function

This fixes those errors.

Also related to this, I noticed that there are several cases where this error shows up:

AssertionError: expected { name: 'Joe',
  age: 20,
  customerId: 'c01',
  bio: undefined,
  approved: undefined,
  joinedAt: undefined } not to have property 'bio'

I'm either completely mistaken or the way that registerProperty is implemented in ModelClass should make that test invalid.  If the object has a field in its schema, that would seem to indicate that it has to have a matching property even if that property has no value ... Or did I miss something there.