Fix flaky test on Windows. (#2278)

pkgs/watcher/test/directory_watcher/file_tests.dart

diff --git a/pkgs/watcher/test/directory_watcher/file_tests.dart b/pkgs/watcher/test/directory_watcher/file_tests.dart
index 912c119..da9a1e9 100644
--- a/pkgs/watcher/test/directory_watcher/file_tests.dart
+++ b/pkgs/watcher/test/directory_watcher/file_tests.dart
@@ -493,7 +493,9 @@
       // there is no file left behind.
       renameDir('watched/x', 'b');
 
-      await expectNoEvents();
+      expect(
+          foldDeletes(await takeEvents(duration: const Duration(seconds: 1))),
+          isEmpty);
     });
 
     test('subdirectory watching is robust against races', () async {

pkgs/watcher/test/utils.dart

diff --git a/pkgs/watcher/test/utils.dart b/pkgs/watcher/test/utils.dart
index 26de5db..073675d 100644
--- a/pkgs/watcher/test/utils.dart
+++ b/pkgs/watcher/test/utils.dart
@@ -205,6 +205,21 @@
   return result;
 }
 
+/// Returns a copy of [events] without events about paths that have a REMOVE
+/// event as the last event.
+///
+/// For example, drops all events for a path with an ADD then a MODIFY then a
+/// REMOVE; keeps all events for a path with ADD, REMOVE, ADD.
+///
+/// This allows tests to avoid flakes due to equivalent but different events
+/// about transient files.
+List<WatchEvent> foldDeletes(List<WatchEvent> events) {
+  final lastEventByPath = {for (final event in events) event.path: event};
+  return events
+      .where((event) => lastEventByPath[event.path]!.type != ChangeType.REMOVE)
+      .toList();
+}
+
 /// Expects that the next event emitted will be for an add event for [path].
 Future expectAddEvent(String path) =>
     _expect(isWatchEvent(ChangeType.ADD, path));