Update function mocking to store results and pass by reference.
Update unit tests to not use external resources.

WARNING: `Unit` class no longer has the method `_hasNetwork()` it has been moved to `Integration`. A better alternative, for unit tests, is to stub function calls in `Mocker::overwriteFunction()` or full classes in `Mocker`.
fix for issue #774

ensure explicit request variables with value 0 are not treated as though they are undefined.