{ lib, python3, poetry2nix, runCommand }:
let
  p = poetry2nix.mkPoetryApplication {
    python = python3;
    src = ./.;
    poetrylock = ./poetry.lock;
    pyproject = ./pyproject.toml;
    overrides = [
      ((
        poetry2nix.defaultPoetryOverrides.overrideOverlay (
          self: super: {
            alembic = super.alembic.overrideAttrs (
              old: {
                TESTING_FOOBAR = 42;
              }
            );
          }
        )
      ).extend (pyself: pysuper: { })) # Test .extend for good measure
    ];
  };
in
runCommand "test"
{ } ''
  x=${builtins.toString (p.python.pkgs.alembic.TESTING_FOOBAR)}
  [ "$x" = "42" ] || exit 1
  mkdir $out
''