(PDOC-2) Refactor tests for 3x function handler

Rework the tests around the 3x function handler. Make them more
verbose by having them them test against multiple examples and by making
the checking of the Registry more details.
(PDOC-2) Refactor tests for host class handler

Update the tests around the host class handler so that they test
several different examples as opposed to just one. Additionally,
refactor the tests so that they are more detailed when it comes to
checking if the Registry is in the correct state after code has been
parsed.