nushell: Add pluggin support tests

tests/modules/programs/nushell/default.nix

@@ -1 +1,4 @@
-{ nushell-example-settings = ./example-settings.nix; }
+{
+  nushell-example-settings = ./example-settings.nix;
+  nushell-plugins = ./plugins.nix;
+}

tests/modules/programs/nushell/plugins.nix

@@ -0,0 +1,22 @@
+{ pkgs, config, ... }:
+
+{
+  programs.nushell = {
+    enable = true;
+    plugins =
+      builtins.attrValues { inherit (pkgs.nushellPlugins) formats gstat; };
+  };
+
+  test.stubs."nushellPlugins.formats" = { };
+
+  nmt.script = let
+    configDir = if pkgs.stdenv.isDarwin && !config.xdg.enable then
+      "home-files/Library/Application Support/nushell"
+    else
+      "home-files/.config/nushell";
+    pluginFile = "${configDir}/plugin.msgpackz";
+
+  in ''
+    assertFileExists "${pluginFile}"
+  '';
+}