Add CI test

.github/workflows/update.yml

@@ -20,3 +20,6 @@ jobs:
         uses: ./.
         with:
           _internal-strict-mode: true
+          flake-dirs: |
+            .
+            test/subflake

test/subflake/flake.lock

@@ -0,0 +1,25 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1716330097,
+        "narHash": "sha256-8BO3B7e3BiyIDsaKA0tY8O88rClYRTjvAp66y+VBUeU=",
+        "rev": "5710852ba686cc1fd0d3b8e22b3117d43ba374c2",
+        "revCount": 629726,
+        "type": "tarball",
+        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.629726%2Brev-5710852ba686cc1fd0d3b8e22b3117d43ba374c2/018fa276-eb5e-762d-b67b-85f281987019/source.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://flakehub.com/f/NixOS/nixpkgs/0.1.%2A.tar.gz"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

test/subflake/flake.nix

@@ -0,0 +1,23 @@
+# Used for testing the flake-dirs parameter
+{
+  description = "update-flake-lock test sub-flake";
+
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
+
+  outputs = { self, nixpkgs }:
+    let
+      supportedSystems = [ "x86_64-linux" "aarch64-darwin" "aarch64-linux" "x86_64-darwin" ];
+      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+        pkgs = import nixpkgs { inherit system; };
+      });
+    in
+    {
+      devShells = forEachSupportedSystem ({ pkgs }: {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            ponysay
+          ];
+        };
+      });
+    };
+}