failing at nix testing

shell

[exarkun@baryon:~/Work/PrivateStorage/PrivateStorageio]$ nix eval --file nixos/lib/tests/test_ini.nix 
error: more arguments are required
Try 'nix --help' for more information.

[exarkun@baryon:~/Work/PrivateStorage/PrivateStorageio]$ nix eval --file nixos/lib/tests/test_ini.nix ''
[ ]

test_ini.nix

let
  pkgs = import <nixpkgs> { };                                                                                                         
  ini = import ../ini.nix;                                                                                                             
in
pkgs.lib.runTests
{ empty =
  { name = "empty";                                                                                                                    
    expected = "";
    expr = ini.allConfigSectionsText { };                                                                                              
  };
}