test: don't use ddebug() before it's defined

test: don't use ddebug() before it's defined

I'm pretty sure this is not the only case, but it's the one I recently
noticed. Even though we call ddebug() from a function, that function is
called before ddebug() is defined, resulting in the same issue as if we
called just ddebug() in its place, i.e.:

..//test-functions: line 276: ddebug: command not found