simplify flake and add checks

flake.nix

@@ -1,42 +1,51 @@
 {
-  inputs = {
-    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1"; # tracks nixpkgs unstable branch
-    flake-parts.url = "github:hercules-ci/flake-parts";
-  };
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1";
 
   outputs =
-    inputs@{ flake-parts, ... }:
-    # https://flake.parts/module-arguments.html
-    flake-parts.lib.mkFlake { inherit inputs; } {
-      flake = {
-        # Put your original flake attributes here.
-      };
+    { self, nixpkgs }:
+    let
       systems = [
-        # systems for which you want to build the `perSystem` attributes
         "x86_64-linux"
         "aarch64-darwin"
       ];
-      perSystem =
-        {
-          config,
-          self',
-          inputs',
-          pkgs,
-          system,
-          ...
-        }:
-        {
-          devShells = {
-            default = pkgs.mkShell {
-              packages = with pkgs; [
-                wrangler
-                nodejs_22
-              ];
-              shellHook = ''
-                export SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
-              '';
-            };
-          };
+      forAllSystems = fn: nixpkgs.lib.genAttrs systems (system: fn nixpkgs.legacyPackages.${system});
+    in
+    {
+      checks = forAllSystems (pkgs: {
+        nix-cache-tests = pkgs.buildNpmPackage {
+          pname = "nix-cache-tests";
+          version = "0.0.0";
+          src = ./nix-cache;
+          npmDepsHash = "sha256-bIujU7pZa1ExCZOMOoxsTeLDSF1GuPN/oMSgiMhY/04=";
+          dontBuild = true;
+          doCheck = true;
+          nativeBuildInputs = [ pkgs.patchelf ];
+          checkPhase = ''
+            runHook preCheck
+            binary=$(find node_modules -path '*/workerd-linux-64/bin/workerd' -type f)
+            if [ -n "$binary" ]; then
+              patchelf --set-interpreter "$(cat ${pkgs.stdenv.cc}/nix-support/dynamic-linker)" "$binary"
+            fi
+            npm test -- --run
+            runHook postCheck
+          '';
+          installPhase = ''
+            touch $out
+          '';
         };
+        devShell = self.devShells.${pkgs.stdenv.hostPlatform.system}.default;
+      });
+
+      devShells = forAllSystems (pkgs: {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            wrangler
+            nodejs_22
+          ];
+          shellHook = ''
+            export SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
+          '';
+        };
+      });
     };
 }