event/filter: hack around data race in the test

event/filter/filter_test.go

 package filter
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 func TestFilters(t *testing.T) {
 	var success bool
@@ -24,6 +27,8 @@ func TestFilters(t *testing.T) {
 	fm.Notify(Generic{Str1: "hello"}, true)
 	fm.Stop()
 
+	time.Sleep(10 * time.Millisecond) // yield to the notifier
+
 	if !success {
 		t.Error("expected 'hello' to be posted")
 	}