test --disk-encryption-keys in sudo test

tests/from-nixos-with-sudo.nix

@@ -6,7 +6,8 @@
   };
   testScript = ''
     start_all()
-    installer.succeed("""
+    installer.succeed("echo super-secret > /tmp/disk-encryption-key")
+    output = installer.succeed("""
       eval $(ssh-agent)
       ssh-add /etc/sshKey
       ${../nixos-remote} \
@@ -14,8 +15,14 @@
         --debug \
         --kexec /etc/nixos-remote/kexec-installer \
         --stop-after-disko \
+        --disk-encryption-keys /tmp/disk-encryption-key \
         --store-paths /etc/nixos-remote/disko /etc/nixos-remote/system-to-install \
         nixos@installed >&2
+      key=$(ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no \
+        root@installed cat /tmp/disk-encryption-key)
+      echo "encryption key: '$key'"
     """)
+
+    assert "encryption key: 'super-secret'" in output, f"output does not contain expected values: {output}"
   '';
 }