To assert static objects, we either have to add a method into the
object under test itself and recompile on a test run with the activated test
method (but also recompile after tests, so that method is gone on
release builds).
Alternatively we can include the whole .c file in our test
infrastructure and save the object in the test directory. So there's no
necessity to clean it up prior to a release build and it's contained
away.
This requires, that the test folder isn't excluded in coveralls.
Rename both functions to make clear, what the difference between the
previous functions _from_file and _from_path is. Also remove the
superfluous `== NULL` checks as these don't match dunst's current style.
