Hi Branden, thank you for the quick response!
I'm happy to report that yes, exporting GROFF_BIN_PATH=. into the nixpkgs test environment works for me and makes the neqn-smoke-test pass. If you think there is value in "enhancing" groff's test suite, I'm all for it, if not, your response has provided me with a very acceptable solution for the groff nixpkgs :) Best Alexis
