diff --git a/code/ch41/microkernel/agent.go b/code/ch41/microkernel/agent.go
index da982d0..4424137 100644
--- a/code/ch41/microkernel/agent.go
+++ b/code/ch41/microkernel/agent.go
@@ -88,6 +88,7 @@ func (agt *Agent) startCollectors() error {
 	var err error
 	var errs CollectorsError
 	var mutex sync.Mutex
+
 	for name, collector := range agt.collectors {
 		go func(name string, collector Collector, ctx context.Context) {
 			defer func() {
@@ -101,6 +102,9 @@ func (agt *Agent) startCollectors() error {
 			}
 		}(name, collector, agt.ctx)
 	}
+	if len(errs.CollectorErrors) == 0 {
+		return nil
+	}
 	return errs
 }
 
@@ -113,6 +117,10 @@ func (agt *Agent) stopCollectors() error {
 				errors.New(name+":"+err.Error()))
 		}
 	}
+	if len(errs.CollectorErrors) == 0 {
+		return nil
+	}
+
 	return errs
 }
 
@@ -125,6 +133,9 @@ func (agt *Agent) destoryCollectors() error {
 				errors.New(name+":"+err.Error()))
 		}
 	}
+	if len(errs.CollectorErrors) == 0 {
+		return nil
+	}
 	return errs
 }
 
diff --git a/code/ch41/microkernel/agent_test.go b/code/ch41/microkernel/agent_test.go
index 400cbad..4beae84 100644
--- a/code/ch41/microkernel/agent_test.go
+++ b/code/ch41/microkernel/agent_test.go
@@ -65,7 +65,9 @@ func TestAgent(t *testing.T) {
 	c2 := NewCollect("c2", "2")
 	agt.RegisterCollector("c1", c1)
 	agt.RegisterCollector("c2", c2)
-	agt.Start()
+	if err := agt.Start(); err != nil {
+		fmt.Printf("start error %v\n", err)
+	}
 	fmt.Println(agt.Start())
 	time.Sleep(time.Second * 1)
 	agt.Stop()