fix test case broadcast

broadcast.go

@@ -53,7 +53,7 @@ func (b *BroadcastString) AddListener(c chan string) chan string {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	if c == nil {
-		c = make(chan string, 0)
+		c = make(chan string, 4)
 	}
 	b.writers[c] = true
 	return c

broadcast_test.go

@@ -3,11 +3,13 @@ package main
 import (
 	"sync"
 	"testing"
+	"time"
 )
 
 func TestBroadcast(t *testing.T) {
 	bs := NewBroadcastString()
 	bs.WriteMessage("hello")
+	time.Sleep(10 * time.Millisecond)
 	c1 := bs.AddListener(nil)
 	go func() {
 		bs.WriteMessage("world")