flake/checks: test extraFiles are in the build

flake-modules/tests.nix

@@ -27,6 +27,8 @@
 
         extend = import ../tests/extend.nix { inherit pkgs makeNixvimWithModule; };
 
+        extra-files = import ../tests/extra-files.nix { inherit pkgs makeNixvimWithModule; };
+
         enable-except-in-tests = import ../tests/enable-except-in-tests.nix {
           inherit pkgs makeNixvimWithModule;
           inherit (self.lib.${system}.check) mkTestDerivationFromNixvimModule;

tests/extra-files.nix

@@ -0,0 +1,32 @@
+{ makeNixvimWithModule, pkgs }:
+let
+  extraFiles = {
+    "one".text = "one";
+    "two".text = "two";
+    "nested/in/dirs/file.txt".text = "nested";
+    "this/file/test.nix".source = ./extra-files.nix;
+  };
+  build = makeNixvimWithModule {
+    module = {
+      inherit extraFiles;
+    };
+  };
+in
+pkgs.runCommand "extra-files-test"
+  {
+    root = build.config.filesPlugin;
+    files = builtins.attrNames extraFiles;
+  }
+  ''
+    for file in $files; do
+      path="$root"/"$file"
+      if [[ -f "$path" ]]; then
+        echo "File $path exists"
+      else
+        echo "File $path is missing"
+        exit 1
+      fi
+    done
+
+    touch $out
+  ''