What do FAA DERs require regarding low-level requirements in DO-178C? Software developed for aircraft needing TA certification pretty much has to be done using a process following RTCA/DO-178C.  My question regards low-level (sometimes called "derived") requirements:

Low-level requirements either refine high-level requirements, or express design decisions.  I've been told a low-level requirement should be traceable to some statement or small block of code, and at DAL C and above, each piece of code needs to be traceable to a low-level requirement.

Do DERs want to see a test corresponding to each low-level requirement, or is that only so for the high-level requirements?  Would it be OK to do testing at a function level ("unit testing") as low-level requirement testing, and are the DERs happy with that?
One thing I would start with is that low level requirements are not the same as derived requirements, although low level requirements can be derived. Derived requirements are requirements that cannot be traced to a higher level requirement.

For verification of DO-178C Level C software, your SVCP will need to completely cover high level and low level requirements as well as attain 100% statement coverage of your code.

As far as what the DER for your project will approve, there really isn't any way for us to know.