The second is a bit odder. For some reason, find-lisp-object-file-name
searches for an internal function definition using TYPE instead of
OBJECT. I would have expected it to use OBJECT like the rest of the
tests do. I see no reason for the current behaviour.

Either the documentation should be changed to clearly indicate the
current behaviour, or the function should be changed so that OBJECTs for
which (subrp (symbol-function OBJECT)) returns t should return
'C-source'.