];
         }

       c) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
         { allowUnfree = true; }
       to ~/.config/nixpkgs/config.nix.

Cannot nix-instantiate `perfect_dark.passthru.tests` because:
error: attribute 'tests' in selection path 'perfect_dark.passthru.tests' not found