diff --git a/cluster/default.nix b/cluster/default.nix
index 97ab73c..548c3af 100644
--- a/cluster/default.nix
+++ b/cluster/default.nix
@@ -16,6 +16,7 @@ lib.evalModules {
     ./lib/port-magic-multi.nix
     ./lib/mesh.nix
     ./lib/secrets.nix
+    ./lib/testing.nix
 
     ./import-services.nix
   ];
diff --git a/cluster/lib/service-module.nix b/cluster/lib/service-module.nix
index 3ef8c98..2fb07e7 100644
--- a/cluster/lib/service-module.nix
+++ b/cluster/lib/service-module.nix
@@ -52,6 +52,24 @@ in
       }));
       default = {};
     };
+    simulacrum = {
+      enable = mkEnableOption "testing this service in the Simulacrum";
+      deps = mkOption {
+        description = "Other services to include.";
+        type = with types; listOf str;
+        default = [];
+      };
+      settings = mkOption {
+        description = "NixOS test configuration.";
+        type = types.deferredModule;
+        default = {};
+      };
+      augments = mkOption {
+        description = "Cluster augments (will be propagated).";
+        type = types.deferredModule;
+        default = {};
+      };
+    };
   };
   config.otherNodes = builtins.mapAttrs (const filterGroup) config.nodes;
 }
diff --git a/cluster/lib/testing.nix b/cluster/lib/testing.nix
new file mode 100644
index 0000000..6c96b37
--- /dev/null
+++ b/cluster/lib/testing.nix
@@ -0,0 +1,9 @@
+{ lib, ... }:
+
+{
+  options.simulacrum = lib.mkOption {
+    description = "Whether we are in the Simulacrum.";
+    type = lib.types.bool;
+    default = false;
+  };
+}