Converts MutatorTest to inherit from common base class
Adds tests for Collection::get() handling missing items
Updates test method name and removes empty lines
Adds test for Collection::isEmpty
Adds test for Collection::getIterator
Clarifies test fixture set up
Adds test for Collection::toArray
Updates ordered book collection fixture
Adds test for Collection::has() with a MongoId parameter
Adds test for Collection::has() with a non-existent MongoId
Adds test for toArray with non-numeric indexes
Adds test for Collection::toArray()
Adds test for Collection::offsetGet() with integer param
Adds test for Collection::offsetGet() with string id param
Adds test for offsetUnset
Adds test for Collection::offsetUnset with a Model param
Adds test for Collection::offsetSet
Adds test for Collection::offsetExists
Adds test for Collection::offsetExists
Adds more Collection::offsetExists tests