tests/emacs: reorganize darwin and linux

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

tests/modules/services/emacs/darwin/basic.nix

@@ -0,0 +1,28 @@
+{ lib, pkgs, ... }:
+
+{
+  nixpkgs.overlays = [
+    (self: super: rec {
+      emacs = pkgs.writeShellScriptBin "dummy-emacs-28.0.5" "" // {
+        outPath = "@emacs@";
+      };
+      emacsPackagesFor =
+        _:
+        lib.makeScope super.newScope (_: {
+          emacsWithPackages = _: emacs;
+        });
+    })
+  ];
+
+  services.emacs = {
+    enable = true;
+  };
+
+  nmt.script = ''
+    serviceFile=LaunchAgents/org.nix-community.home.emacs.plist
+
+    assertFileExists "$serviceFile"
+
+    assertFileContent "$serviceFile" ${./expected-agent.plist}
+  '';
+}