add unittests and bug fix

lib/timewheel/delay_test.go

@@ -0,0 +1,20 @@
+package timewheel
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDelay(t *testing.T) {
+	ch := make(chan time.Time)
+	beginTime := time.Now()
+	Delay(time.Second, "", func() {
+		ch <- time.Now()
+	})
+	execAt := <-ch
+	delayDuration := execAt.Sub(beginTime)
+	// usually 1.0~2.0 s
+	if delayDuration < time.Second || delayDuration > 3*time.Second {
+		t.Error("wrong execute time")
+	}
+}