What code won't benefit from unit testing ?

If you don't know what to test, then you don't know what you are implementing. Find what that is, clarify it and pin it down with a test then move on to the implementation to make it happen.

If you don't know what the output is like, then do some exploratory throw-away work to know a little more. Then write the test that you would've written if you knew what the output is like.

tackle your problems one a at a time, not knowing what to test is not a good enough excuse to not test first.

Make it Work - Make it Right - Make it Fast (while still under the protection of your first-written test)