Add test coverage for file watcher and symlinks.

pkgs/watcher/test/file_watcher/link_tests.dart

@@ -0,0 +1,168 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+
+import '../utils.dart';
+
+void linkTests({required bool isNative}) {
+  setUp(() async {
+    writeFile('target.txt');
+    writeLink(link: 'link.txt', target: 'target.txt');
+  });
+
+  test("doesn't notify if nothing is modified", () async {
+    await startWatcher(path: 'link.txt');
+    await expectNoEvents();
+  });
+
+  test('notifies when a link is overwritten with an identical file', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('link.txt');
+    await expectModifyEvent('link.txt');
+  });
+
+  test('notifies when a link is overwritten with a different file', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('link.txt', contents: 'modified');
+    await expectModifyEvent('link.txt');
+  });
+
+  test(
+    'notifies when a link target is overwritten with an identical file',
+    () async {
+      await startWatcher(path: 'link.txt');
+      writeFile('target.txt');
+
+      // TODO(davidmorgan): reconcile differences.
+      if (isNative) {
+        await expectModifyEvent('link.txt');
+      } else {
+        await expectNoEvents();
+      }
+    },
+  );
+
+  test('notifies when a link target is modified', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('target.txt', contents: 'modified');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectModifyEvent('link.txt');
+    } else {
+      await expectNoEvents();
+    }
+  });
+
+  test('notifies when a link is removed', () async {
+    await startWatcher(path: 'link.txt');
+    deleteFile('link.txt');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectNoEvents();
+    } else {
+      await expectRemoveEvent('link.txt');
+    }
+  });
+
+  test('notifies when a link target is removed', () async {
+    await startWatcher(path: 'link.txt');
+    deleteFile('target.txt');
+    await expectRemoveEvent('link.txt');
+  });
+
+  test('notifies when a link target is modified multiple times', () async {
+    await startWatcher(path: 'link.txt');
+
+    writeFile('target.txt', contents: 'modified');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectModifyEvent('link.txt');
+    } else {
+      await expectNoEvents();
+    }
+
+    writeFile('target.txt', contents: 'modified again');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectModifyEvent('link.txt');
+    } else {
+      await expectNoEvents();
+    }
+  });
+
+  test('notifies when a link is moved away', () async {
+    await startWatcher(path: 'link.txt');
+    renameFile('link.txt', 'new.txt');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectNoEvents();
+    } else {
+      await expectRemoveEvent('link.txt');
+    }
+  });
+
+  test('notifies when a link target is moved away', () async {
+    await startWatcher(path: 'link.txt');
+    renameFile('target.txt', 'new.txt');
+    await expectRemoveEvent('link.txt');
+  });
+
+  test('notifies when an identical file is moved over the link', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('old.txt');
+    renameFile('old.txt', 'link.txt');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectNoEvents();
+    } else {
+      await expectModifyEvent('link.txt');
+    }
+  });
+
+  test('notifies when an different file is moved over the link', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('old.txt', contents: 'modified');
+    renameFile('old.txt', 'link.txt');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectNoEvents();
+    } else {
+      await expectModifyEvent('link.txt');
+    }
+  });
+
+  test('notifies when an identical file is moved over the target', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('old.txt');
+    renameFile('old.txt', 'target.txt');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectModifyEvent('link.txt');
+    } else {
+      await expectNoEvents();
+    }
+  });
+
+  test('notifies when a different file is moved over the target', () async {
+    await startWatcher(path: 'link.txt');
+    writeFile('old.txt', contents: 'modified');
+    renameFile('old.txt', 'target.txt');
+
+    // TODO(davidmorgan): reconcile differences.
+    if (isNative) {
+      await expectModifyEvent('link.txt');
+    } else {
+      await expectNoEvents();
+    }
+  });
+}

pkgs/watcher/test/utils.dart

@@ -246,6 +246,34 @@ void writeFile(String path, {String? contents, bool? updateModified}) {
   }
 }
 
+/// Schedules writing a file in the sandbox at [link] pointing to [target].
+///
+/// If [updateModified] is `false`, the mock file modification time is not
+/// changed.
+void writeLink({
+  required String link,
+  required String target,
+  bool? updateModified,
+}) {
+  updateModified ??= true;
+
+  var fullPath = p.join(d.sandbox, link);
+
+  // Create any needed subdirectories.
+  var dir = Directory(p.dirname(fullPath));
+  if (!dir.existsSync()) {
+    dir.createSync(recursive: true);
+  }
+
+  Link(fullPath).createSync(target);
+
+  if (updateModified) {
+    link = p.normalize(link);
+
+    _mockFileModificationTimes[link] = _nextTimestamp++;
+  }
+}
+
 /// Schedules deleting a file in the sandbox at [path].
 void deleteFile(String path) {
   File(p.join(d.sandbox, path)).deleteSync();