flake.nix: run tests against pinned nixpkgs

and migrate to the new runTest, which evaluates much faster.

flake.nix

@@ -21,27 +21,38 @@
     releases = [
       {
         name = "unstable";
+        nixpkgs = nixpkgs;
         pkgs = nixpkgs.legacyPackages.${system};
       }
       {
         name = "24.11";
+        nixpkgs = nixpkgs-24_11;
         pkgs = nixpkgs-24_11.legacyPackages.${system};
       }
     ];
     testNames = [
-      "internal"
-      "external"
       "clamav"
-      "multiple"
+      "external"
+      "internal"
       "ldap"
+      "multiple"
     ];
-    genTest = testName: release: {
-      "name"= "${testName}-${builtins.replaceStrings ["."] ["_"] release.name}";
-      "value"= import (./tests/. + "/${testName}.nix") {
-        pkgs = release.pkgs;
-        inherit blobs;
+
+    genTest = testName: release: let
+      pkgs = release.pkgs;
+      nixos-lib = import (release.nixpkgs + "/nixos/lib") {
+        inherit (pkgs) lib;
+      };
+    in {
+      name = "${testName}-${builtins.replaceStrings ["."] ["_"] release.name}";
+      value = nixos-lib.runTest {
+        hostPkgs = pkgs;
+        imports = [ ./tests/${testName}.nix ];
+        _module.args = { inherit blobs; };
+        extraBaseModules.imports = [ ./default.nix ];
       };
     };
+
     # Generate an attribute set such as
     # {
     #   external-unstable = <derivation>;