test,fs: test fs.watch for filename

test/parallel/test-fs-watch.js

@@ -0,0 +1,77 @@
+'use strict';
+const common = require('../common');
+
+// tests if `filename` is provided to watcher on supported platforms
+
+const fs = require('fs');
+const assert = require('assert');
+const { join } = require('path');
+
+class WatchTestCase {
+  constructor(shouldInclude, dirName, fileName, field) {
+    this.dirName = dirName;
+    this.fileName = fileName;
+    this.field = field;
+    this.shouldSkip = !shouldInclude;
+  }
+  get dirPath() { return join(common.tmpDir, this.dirName); }
+  get filePath() { return join(this.dirPath, this.fileName); }
+}
+
+const cases = [
+  // Watch on a directory should callback with a filename on supported systems
+  new WatchTestCase(
+    common.isLinux || common.isOSX || common.isWindows || common.isAix,
+    'watch1',
+    'foo',
+    'filePath'
+  ),
+  // Watch on a file should callback with a filename on supported systems
+  new WatchTestCase(
+    common.isLinux || common.isOSX || common.isWindows,
+    'watch2',
+    'bar',
+    'dirPath'
+  )
+];
+
+common.refreshTmpDir();
+
+for (const testCase of cases) {
+  if (testCase.shouldSkip) continue;
+  fs.mkdirSync(testCase.dirPath);
+  // long content so it's actually flushed.
+  const content1 = Date.now() + testCase.fileName.toLowerCase().repeat(1e4);
+  fs.writeFileSync(testCase.filePath, content1);
+
+  let interval;
+  const watcher = fs.watch(testCase[testCase.field]);
+  watcher.on('error', (err) => {
+    if (interval) {
+      clearInterval(interval);
+      interval = null;
+    }
+    assert.fail(err);
+  });
+  watcher.on('change', common.mustCall(function(eventType, argFilename) {
+    if (interval) {
+      clearInterval(interval);
+      interval = null;
+    }
+    if (common.isOSX)
+      assert.strictEqual(['rename', 'change'].includes(eventType), true);
+    else
+      assert.strictEqual(eventType, 'change');
+    assert.strictEqual(argFilename, testCase.fileName);
+
+    // end of test case
+    watcher.close();
+  }));
+
+  // long content so it's actually flushed. toUpperCase so there's real change.
+  const content2 = Date.now() + testCase.fileName.toUpperCase().repeat(1e4);
+  interval = setInterval(() => {
+    fs.writeFileSync(testCase.filePath, '');
+    fs.writeFileSync(testCase.filePath, content2);
+  }, 100);
+}