Merge pull request #265836 from hercules-ci/nixosTests-no-surprises

            key = "nodes.nix-pkgs";

            config = optionalAttrs (!config.node.pkgsReadOnly) (

              mkIf (!options.nixpkgs.pkgs.isDefined) {

                # Ensure we do not use aliases. Ideally this is only set

                # when the test framework is used by Nixpkgs NixOS tests.

                nixpkgs.config.allowAliases = false;

                # TODO: switch to nixpkgs.hostPlatform and make sure containers-imperative test still evaluates.

                nixpkgs.system = hostPkgs.stdenv.hostPlatform.system;

              }