Add scenarios showing problem with separate code/test

Non-stdlib kinda works (though if you look at what is actually
happening it's not ideal - and will break coverage).  If mocking
stdlib packages, then it doesn't work at all.

This is the cause of issue #39.
Start tracking test deps

Some of the tests need extra packages installed.  Show that the deps
are missing instead of failing the test.
Example has some deps too ...
Skip another broken test file

The Go source seems to have aquired another deliberately broken test
package.  So we need to skip this one too when we check we can parse
the whole tree.