nixos/all-tests.nix: Add readOnlyPkgs module

              virtualisation.qemu.package = testModuleArgs.config.qemu.package;

            })

          ({

            key = "nodes.nix-pkgs";

            config = {

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

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

    runTestOn

    ;

  # Using a single instance of nixpkgs makes test evaluation faster.

  # To make sure we don't accidentally depend on a modified pkgs, we make the

  # related options read-only. We need to test the right configuration.

  #

  # If your service depends on a nixpkgs setting, first try to avoid that, but

  # otherwise, you can remove the readOnlyPkgs import and test your service as

  # usual.

  readOnlyPkgs =

    # TODO: We currently accept this for nixosTests, so that the `pkgs` argument

    #       is consistent with `pkgs` in `pkgs.nixosTests`. Can we reinitialize

    #       it with `allowAliases = false`?

    # warnIf pkgs.config.allowAliases "nixosTests: pkgs includes aliases."

    {

      _class = "nixosTest";

      defaults = {

        nixpkgs.pkgs = pkgs;

        imports = [ ../modules/misc/nixpkgs/read-only.nix ];

        disabledModules = [{ key = "nodes.nix-pkgs"; }];

      };

    };

in {

  # Testing the test driver