vfs: fix RealFSProvider watchFile listener

lib/internal/vfs/provider.js

@@ -597,9 +597,10 @@ class VirtualProvider {
    * @param {object} [options] Watch options
    * @param {number} [options.interval] Polling interval in ms (default: 5007)
    * @param {boolean} [options.persistent] Whether the watcher should prevent exit
+   * @param {Function} [listener] Change listener
    * @throws {ERR_METHOD_NOT_IMPLEMENTED} When not overridden by subclass
    */
-  watchFile(path, options) {
+  watchFile(path, options, listener) {
     throw new ERR_METHOD_NOT_IMPLEMENTED('watchFile');
   }
 

lib/internal/vfs/providers/real.js

@@ -543,9 +543,9 @@ class RealFSProvider extends VirtualProvider {
     return fs.promises.watch(realPath, options);
   }
 
-  watchFile(vfsPath, options) {
+  watchFile(vfsPath, options, listener) {
     const realPath = this.#resolvePath(vfsPath);
-    return fs.watchFile(realPath, options, () => {});
+    return fs.watchFile(realPath, options, listener);
   }
 
   unwatchFile(vfsPath, listener) {

test/parallel/test-vfs-real-provider-watch.js

@@ -1,3 +1,3 @@
 // Flags: --experimental-vfs
 'use strict';
 
@@ -38,3 +38,14 @@
   myVfs.watchFile('/wf.txt', { persistent: false }, listener);
   myVfs.unwatchFile('/wf.txt', listener);
 }
+
+// watchFile listener fires on change
+(async () => {
+  fs.writeFileSync(path.join(root, 'wf2.txt'), 'a');
+  const fired = new Promise((resolve) => {
+    myVfs.watchFile('/wf2.txt', { interval: 25 }, common.mustCall(resolve));
+  });
+  fs.writeFileSync(path.join(root, 'wf2.txt'), 'b');
+  await fired;
+  myVfs.unwatchFile('/wf2.txt');
+})().then(common.mustCall());