nixos/kmonad: add a basic nixos test

nixos/tests/all-tests.nix

@@ -520,6 +520,7 @@ in {
   keyd = handleTest ./keyd.nix {};
   keymap = handleTest ./keymap.nix {};
   kimai = handleTest ./kimai.nix {};
+  kmonad = runTest ./kmonad.nix;
   knot = handleTest ./knot.nix {};
   komga = handleTest ./komga.nix {};
   krb5 = discoverTests (import ./krb5);

nixos/tests/kmonad.nix

@@ -0,0 +1,47 @@
+{ lib, ... }:
+
+{
+  name = "kmonad";
+
+  meta = {
+    maintainers = with lib.maintainers; [ linj ];
+  };
+
+  nodes = {
+    machine = {
+      services.kmonad = {
+        enable = true;
+        keyboards = {
+          defaultKbd = {
+            device = "/dev/input/by-id/vm-default-kbd";
+            defcfg = {
+              enable = true;
+              fallthrough = true;
+            };
+            config = ''
+              (defsrc :name default-src
+                1)
+              (deflayer default-layer :source default-src
+                @T2)
+              (defalias
+                T2 2)
+            '';
+          };
+        };
+      };
+
+      # make a determinate symlink to the default vm keyboard for kmonad to use
+      services.udev.extraRules = ''
+        ACTION=="add", KERNEL=="event*", SUBSYSTEM=="input", ATTRS{name}=="QEMU Virtio Keyboard", ATTRS{id/product}=="0001", ATTRS{id/vendor}=="0627", SYMLINK+="input/by-id/vm-default-kbd"
+      '';
+    };
+  };
+
+  testScript = ''
+    service_name = "kmonad-defaultKbd"
+    machine.wait_for_unit(f"{service_name}.service")
+
+    with subtest("kmonad is running"):
+         machine.succeed(f"systemctl status {service_name}")
+  '';
+}

pkgs/development/haskell-modules/configuration-nix.nix

@@ -1478,7 +1478,14 @@ self: super: builtins.intersectAttrs super {
   # cause actual problems in dependent packages, see https://github.com/lehins/pvar/issues/4
   pvar = dontCheck super.pvar;
 
-  kmonad = enableSeparateBinOutput super.kmonad;
+  kmonad = lib.pipe super.kmonad [
+    enableSeparateBinOutput
+    (overrideCabal (drv: {
+      passthru = lib.recursiveUpdate
+        drv.passthru or { }
+        { tests.nixos = pkgs.nixosTests.kmonad; };
+    }))
+  ];
 
   xmobar = enableSeparateBinOutput super.xmobar;