test: make fs watch test more stable

PR-URL: #41715
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/pummel/test-fs-watch-non-recursive.js

@@ -28,7 +28,7 @@ if (common.isIBMi) {
 
 const path = require('path');
 const fs = require('fs');
-
+const assert = require('assert');
 const tmpdir = require('../common/tmpdir');
 tmpdir.refresh();
 
@@ -38,13 +38,14 @@ const filepath = path.join(testsubdir, 'watch.txt');
 
 fs.mkdirSync(testsubdir, 0o700);
 
-// Need a grace period, else the mkdirSync() above fires off an event.
-setTimeout(function() {
-  const watcher = fs.watch(testDir, { persistent: true }, common.mustNotCall());
-  setTimeout(function() {
-    fs.writeFileSync(filepath, 'test');
-  }, 100);
-  setTimeout(function() {
-    watcher.close();
-  }, 500);
-}, 50);
+const watcher = fs.watch(testDir, { persistent: true }, (event, filename) => {
+  // This function may be called with the directory depending on timing but
+  // must not be called with the file..
+  assert.strictEqual(filename, 'testsubdir');
+});
+setTimeout(() => {
+  fs.writeFileSync(filepath, 'test');
+}, 100);
+setTimeout(() => {
+  watcher.close();
+}, 500);