cmd/sharefs/test: check option handling

This verifies behaviour related to setuid/setgid when starting as root.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/sharefs/test/configuration.nix

@@ -1,4 +1,4 @@
-{ pkgs, ... }:
+{ pkgs, config, ... }:
 {
   users.users = {
     alice = {
@@ -14,8 +14,13 @@
   # Automatically login on tty1 as a normal user:
   services.getty.autologinUser = "alice";
 
-  # For benchmarking sharefs:
-  environment.systemPackages = [ pkgs.fsmark ];
+  environment = {
+    # For benchmarking sharefs:
+    systemPackages = [ pkgs.fsmark ];
+
+    # For sharefs option checks without adding to PATH:
+    etc.sharefs.source = "${config.environment.hakurei.package}/libexec/sharefs";
+  };
 
   virtualisation = {
     diskSize = 6 * 1024;