depth crashes when it is unable to resolve an imported package

[KyleBanks]

This may be fine for typical use, but for testing package imports it's particularly troubling. Consider the following:

mypkg 
    - vendoredpkg
         - testdep

When resolving dependencies most package managers do not resolve secondary dependencies that are only required for testing. If mypkg depends on vendoredpkg that's fine, but running depth with -test will try to resolve it's testdep, which likely won't exist.

I think in the case of test packages only, depth could output something like so:

mypkg 
    - vendoredpkg
         - testdep (UNRESOLVED)