flake: expose tests as checks output

flake.nix

@@ -235,6 +235,10 @@
         buildPlatform = builtins.currentSystem;
       };
       lib = import ./modules/lib.nix { inherit inputs pkgs service_configs; };
+      testSuite = import ./tests/tests.nix {
+        inherit pkgs lib inputs;
+        config = self.nixosConfigurations.muffin.config;
+      };
     in
     {
       formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixfmt-tree;
@@ -319,14 +323,9 @@
         };
       };
 
-      packages.${system} =
-        let
-          testSuite = import ./tests/tests.nix {
-            inherit pkgs lib inputs;
-            config = self.nixosConfigurations.muffin.config;
-          };
-        in
-        {
+      checks.${system} = testSuite;
+
+      packages.${system} = {
           tests = pkgs.linkFarm "all-tests" (
             pkgs.lib.mapAttrsToList (name: test: {
               name = name;