diff --git a/modules/testing/default.nix b/modules/testing/default.nix
index b813b3d..09c7a11 100644
--- a/modules/testing/default.nix
+++ b/modules/testing/default.nix
@@ -53,6 +53,7 @@ in
             description = "Default to apply to test";
             type = types.unspecified;
             default = { };
+            apply = default: { _file = "testing.defaults"; } // default;
           };
         };
       }));
diff --git a/modules/testing/docker.nix b/modules/testing/docker.nix
index 63342f9..7b2adbd 100644
--- a/modules/testing/docker.nix
+++ b/modules/testing/docker.nix
@@ -40,6 +40,7 @@ in
   config.testing.defaults = [{
     features = [ "docker" ];
     default = {
+      _file = "testing.docker.registryUrl";
       docker.registry.url = cfg.registryUrl;
     };
   }];