Faster TestWatchList/race

This test took over 2.5 seconds, and the entire test suite went from ~7s
to ~9.5s on my laptop. So make it a bit faster.

(Manually verified it reproduces the bug prior to dab9dde)

fsnotify_test.go

diff --git a/fsnotify_test.go b/fsnotify_test.go
index 451c828..4101d3d 100644
--- a/fsnotify_test.go
+++ b/fsnotify_test.go
@@ -885,32 +885,33 @@
 		t.Parallel()
 
 		tmp := t.TempDir()
+		w := newCollector(t, tmp)
+		w.collect(t)
 
-		w := newWatcher(t, tmp)
-		defer w.Close()
-
-		stop := make(chan struct{})
-		done := make(chan struct{})
 		go func() {
-			defer close(done)
 			for {
 				select {
-				case <-stop:
+				case <-w.done:
 					return
 				default:
-					// Just make sure it doesn't race, don't need to checkout output.
-					_ = w.WatchList()
+					_ = w.w.WatchList()
+					time.Sleep(10 * time.Millisecond)
 				}
 			}
 		}()
 
-		for i := range 50 {
-			dir := filepath.Join(tmp, fmt.Sprintf("d%d", i))
-			mkdir(t, dir)
-			addWatch(t, w, dir)
+		var wg sync.WaitGroup
+		wg.Add(20)
+		for i := range 20 {
+			go func() {
+				defer wg.Done()
+				dir := filepath.Join(tmp, fmt.Sprintf("d%d", i))
+				mkdir(t, dir)
+				addWatch(t, w.w, dir)
+			}()
 		}
-		close(stop)
-		<-done
+		wg.Wait()
+		w.stop(t)
 	})
 }
 

helpers_test.go

diff --git a/helpers_test.go b/helpers_test.go
index e664505..a4aa255 100644
--- a/helpers_test.go
+++ b/helpers_test.go
@@ -425,15 +425,15 @@
 			select {
 			case e, ok := <-w.w.Errors:
 				if !ok {
-					w.done <- struct{}{}
+					close(w.done)
 					return
 				}
 				t.Errorf("eventCollector: unexpected error on Errors chan: %s", e)
-				w.done <- struct{}{}
+				close(w.done)
 				return
 			case e, ok := <-w.w.Events:
 				if !ok {
-					w.done <- struct{}{}
+					close(w.done)
 					return
 				}
 				w.mu.Lock()