Last item for beta -- new MAIN_DOCUMENT test

Currently the unit tests fail, each of them, since there is a new test
result titled "MAIN_DOCUMENT". Just checking that we're all OK with
introducing this new element to cover, I assume, errors that occur in
the document as a whole? we don't really define a "MAIN_DOCUMENT" test
in mobileOK Basic and just imply that if the test document can't be
retrieved, the other test results don't have meaning.

I don't mind the current setup, just checking for opinion on this
before we bless this as a beta.

Sean