depot/third_party/nixpkgs/nixos/tests/containers-custom-pkgs.nix

import ./make-test-python.nix (
  { pkgs, lib, ... }:
  let

    customPkgs = pkgs.appendOverlays [
      (self: super: {
        hello = super.hello.overrideAttrs (old: {
          name = "custom-hello";
        });
      })
    ];

  in
  {
    name = "containers-custom-pkgs";
    meta = {
      maintainers = with lib.maintainers; [ erikarvstedt ];
    };

    nodes.machine =
      { config, ... }:
      {
        assertions =
          let
            helloName = (builtins.head config.containers.test.config.system.extraDependencies).name;
          in
          [
            {
              assertion = helloName == "custom-hello";
              message = "Unexpected value: ${helloName}";
            }
          ];

        containers.test = {
          autoStart = true;
          config =
            { pkgs, config, ... }:
            {
              nixpkgs.pkgs = customPkgs;
              system.extraDependencies = [ pkgs.hello ];
            };
        };
      };

    # This test only consists of evaluating the test machine
    testScript = "pass";
  }
)