diff --git a/stylix/testbed/autoload.nix b/stylix/testbed/autoload.nix
new file mode 100644
index 000000000..29f5f1a2c
--- /dev/null
+++ b/stylix/testbed/autoload.nix
@@ -0,0 +1,118 @@
+{
+  pkgs,
+  lib,
+  testbedFieldSeparator ? ":",
+}:
+let
+  isEnabled = pkgs.callPackage ./is-enabled.nix { };
+
+  # Describes all testbed modules loaded from the modules directory.
+  # A list of attrsets, each containing: { module, path, name }
+  testbeds = lib.pipe ../../modules [
+    builtins.readDir
+    builtins.attrNames
+    (builtins.concatMap (
+      module:
+      let
+        testbeds = ../../modules/${module}/testbeds;
+        files = lib.optionalAttrs (builtins.pathExists testbeds) (
+          builtins.readDir testbeds
+        );
+      in
+      lib.mapAttrsToList (
+        testbed: type:
+        let
+          path = testbeds + "/${testbed}";
+          pathStr = toString path;
+        in
+        if type != "regular" then
+          throw "${pathStr} must be regular: ${type}"
+
+        else if !lib.hasSuffix ".nix" testbed then
+          throw "testbed must be a Nix file: ${pathStr}"
+
+        else if testbed == ".nix" then
+          throw "testbed must have a name: ${pathStr}"
+
+        else
+          {
+            inherit module path;
+            name = lib.removeSuffix ".nix" testbed;
+          }
+      ) files
+    ))
+  ];
+
+  # Import all the testbed themes
+  themes = lib.pipe ./themes [
+    builtins.readDir
+    (lib.filterAttrs (name: _: lib.strings.hasSuffix ".nix" name))
+    (builtins.mapAttrs (
+      name: type:
+      lib.throwIfNot (type == "regular")
+        "Unexpected filetype in testbed themes: ${toString ./themes/${name}} is a ${type}."
+        ./themes/${name}
+    ))
+    (lib.mapAttrs' (name: lib.nameValuePair (lib.strings.removeSuffix ".nix" name)))
+  ];
+
+  # Construct a NixOS module for the testbed+theme combination.
+  #
+  # If the testbed module is enabled, returns an attrset containing it:
+  # { «name» = «modele»; }
+  #
+  # Returns an empty attrset if the testbed module is not enabled.
+  # { }
+  makeTestbedModule =
+    testbed: themeName: themeModule:
+    let
+      joinFields = builtins.concatStringsSep testbedFieldSeparator;
+
+      fields =
+        map
+          (
+            field:
+            lib.throwIf (lib.hasInfix testbedFieldSeparator field)
+              "testbed field must not contain the '${testbedFieldSeparator}' testbed field separator: ${field}"
+              field
+          )
+          [
+            "testbed"
+            testbed.name
+            themeName
+          ];
+
+      name = joinFields fields;
+    in
+    lib.optionalAttrs (isEnabled testbed.path) {
+      ${name} = {
+        # Unique key for de-duplication
+        key = joinFields [
+          (toString ./.)
+          name
+        ];
+
+        # Location displayed in errors
+        _file = name;
+
+        # Avoid accidental imports, e.g. in submodules or home-manager
+        _class = "nixos";
+
+        imports = [
+          testbed.path
+          themeModule
+        ];
+
+        config.system.name = name;
+      };
+    };
+
+  # Generates a copy of each testbed for each of the imported themes.
+  # I.e. a testbeds*themes matrix
+  makeTestbeds = testbed: lib.mapAttrsToList (makeTestbedModule testbed) themes;
+in
+# Testbeds are merged using lib.attrsets.unionOfDisjoint to throw an error if
+# any name collides.
+builtins.foldl' lib.attrsets.unionOfDisjoint { } (
+  builtins.concatMap makeTestbeds testbeds
+)
diff --git a/stylix/testbed/default.nix b/stylix/testbed/default.nix
index bcb61484b..68014ca0b 100644
--- a/stylix/testbed/default.nix
+++ b/stylix/testbed/default.nix
@@ -2,63 +2,13 @@
   pkgs,
   inputs,
   lib,
-  testbedFieldSeparator ? ":",
+  modules ? import ./autoload.nix { inherit pkgs lib; },
 }:
 
 let
-  isEnabled = pkgs.callPackage ./is-enabled.nix { };
-
-  autoload = lib.pipe ../../modules [
-    builtins.readDir
-    builtins.attrNames
-    (builtins.concatMap (
-      module:
-      let
-        testbeds = ../../modules/${module}/testbeds;
-        files = lib.optionalAttrs (builtins.pathExists testbeds) (
-          builtins.readDir testbeds
-        );
-      in
-      lib.mapAttrsToList (
-        testbed: type:
-        let
-          path = testbeds + "/${testbed}";
-          pathStr = toString path;
-        in
-        if type != "regular" then
-          throw "${pathStr} must be regular: ${type}"
-
-        else if !lib.hasSuffix ".nix" testbed then
-          throw "testbed must be a Nix file: ${pathStr}"
-
-        else if testbed == ".nix" then
-          throw "testbed must have a name: ${pathStr}"
-
-        else
-          {
-            inherit module path;
-            name = lib.removeSuffix ".nix" testbed;
-          }
-      ) files
-    ))
-  ];
-
   makeTestbed =
-    testbed: themeName: themeModule:
+    name: testbed:
     let
-      name =
-        lib.concatMapStringsSep testbedFieldSeparator
-          (
-            field:
-            lib.throwIf (lib.hasInfix testbedFieldSeparator field)
-              "testbed field must not contain the '${testbedFieldSeparator}' testbed field separator: ${field}"
-              field
-          )
-          [
-            "testbed"
-            testbed.name
-            themeName
-          ];
 
       system = lib.nixosSystem {
         inherit (pkgs) system;
@@ -69,54 +19,27 @@ let
           ./modules/application.nix
           inputs.self.nixosModules.stylix
           inputs.home-manager.nixosModules.home-manager
-          testbed.path
-          themeModule
-          { system.name = name; }
+          testbed
         ];
       };
-
-      script = pkgs.writeShellApplication {
-        inherit name;
-        text = ''
-          cleanup() {
-            if rm --recursive "$directory"; then
-              printf '%s\n' 'Virtualisation disk image removed.'
-            fi
-          }
-
-          # We create a temporary directory rather than a temporary file, since
-          # temporary files are created empty and are not valid disk images.
-          directory="$(mktemp --directory)"
-          trap cleanup EXIT
-
-          NIX_DISK_IMAGE="$directory/nixos.qcow2" \
-            ${lib.getExe system.config.system.build.vm}
-        '';
-      };
     in
-    lib.optionalAttrs (isEnabled testbed.path) {
-      ${name} = script;
+    pkgs.writeShellApplication {
+      inherit name;
+      text = ''
+        cleanup() {
+          if rm --recursive "$directory"; then
+            printf '%s\n' 'Virtualisation disk image removed.'
+          fi
+        }
+
+        # We create a temporary directory rather than a temporary file, since
+        # temporary files are created empty and are not valid disk images.
+        directory="$(mktemp --directory)"
+        trap cleanup EXIT
+
+        NIX_DISK_IMAGE="$directory/nixos.qcow2" \
+          ${lib.getExe system.config.system.build.vm}
+      '';
     };
-
-  # Import all the testbed themes
-  themes = lib.pipe ./themes [
-    builtins.readDir
-    (lib.filterAttrs (name: _: lib.strings.hasSuffix ".nix" name))
-    (builtins.mapAttrs (
-      name: type:
-      lib.throwIfNot (type == "regular")
-        "Unexpected filetype in testbed themes: ${toString ./themes/${name}} is a ${type}."
-        ./themes/${name}
-    ))
-    (lib.mapAttrs' (name: lib.nameValuePair (lib.strings.removeSuffix ".nix" name)))
-  ];
-
-  # This generates a copy of each testbed for each of the imported themes.
-  makeTestbeds = testbed: lib.mapAttrsToList (makeTestbed testbed) themes;
-
 in
-# Testbeds are merged using lib.attrsets.unionOfDisjoint to throw an error if
-# testbed names collide.
-builtins.foldl' lib.attrsets.unionOfDisjoint { } (
-  builtins.concatMap makeTestbeds autoload
-)
+builtins.mapAttrs makeTestbed modules