Create a helper function to create mocks of database results

## Create a helper function that can be used to mock iterator objects (e.g., db results)

### Tasks
 - Add a helper function in MapperTestCase that accepts an array of associative arrays representing a mocked database result and implements mock result callback functions that implement the iterator interface using the passed-in values. See link below for an example on how to do this.

### Additional Notes
 - http://www.davegardner.me.uk/blog/2011/03/04/mocking-iterator-with-phpunit/
Sometimes this needs to not be null (namely, on `INSERT`).