htop: use dummy package in tests

tests/modules/programs/htop/empty-settings.nix

@@ -6,6 +6,9 @@ with lib;
   config = {
     programs.htop.enable = true;
 
+    nixpkgs.overlays =
+      [ (self: super: { htop = pkgs.writeScriptBin "dummy" ""; }) ];
+
     nmt.script = ''
       assertPathNotExists home-files/.config/htop
     '';

tests/modules/programs/htop/example-settings.nix

@@ -36,6 +36,9 @@ with lib;
           (text "Systemd")
         ]);
 
+    nixpkgs.overlays =
+      [ (self: super: { htop = pkgs.writeScriptBin "dummy" ""; }) ];
+
     nmt.script = ''
       htoprc=home-files/.config/htop/htoprc
       assertFileExists $htoprc

tests/modules/programs/htop/settings-without-fields.nix

@@ -7,6 +7,9 @@ with lib;
     programs.htop.enable = true;
     programs.htop.settings = { color_scheme = 6; };
 
+    nixpkgs.overlays =
+      [ (self: super: { htop = pkgs.writeScriptBin "dummy" ""; }) ];
+
     # Test that the 'fields' key is written in addition to the customized
     # settings or htop won't read the options.
     nmt.script = ''