lib/tests: More functionTo tests

lib/tests/modules/functionTo/merging-list.nix

@@ -0,0 +1,24 @@
+{ lib, config, ... }:
+let
+  inherit (lib) types;
+in {
+  options = {
+    fun = lib.mkOption {
+      type = types.functionTo (types.listOf types.str);
+    };
+
+    result = lib.mkOption {
+      type = types.str;
+      default = toString (config.fun {
+        a = "a";
+        b = "b";
+        c = "c";
+      });
+    };
+  };
+
+  config.fun = lib.mkMerge [
+    (input: [ input.a ])
+    (input: [ input.b ])
+  ];
+}