modify unit test of producer

client/src/test/java/org/apache/rocketmq/client/producer/DefaultMQProducerTest.java

@@ -105,7 +105,9 @@ public class DefaultMQProducerTest {
 
         when(mQClientAPIImpl.sendMessage(anyString(), anyString(), any(Message.class), any(SendMessageRequestHeader.class), anyLong(), any(CommunicationMode.class),
             nullable(SendMessageContext.class), any(DefaultMQProducerImpl.class))).thenCallRealMethod();
-
+        when(mQClientAPIImpl.sendMessage(anyString(), anyString(), any(Message.class), any(SendMessageRequestHeader.class), anyLong(), any(CommunicationMode.class),
+            nullable(SendCallback.class), nullable(TopicPublishInfo.class), nullable(MQClientInstance.class), anyInt(), nullable(SendMessageContext.class), any(DefaultMQProducerImpl.class)))
+            .thenReturn(createSendResult(SendStatus.SEND_OK));
         when(mQClientAPIImpl.sendMessage(anyString(), anyString(), any(Message.class), any(SendMessageRequestHeader.class), anyLong(), any(CommunicationMode.class),
             any(SendCallback.class), nullable(TopicPublishInfo.class), any(MQClientInstance.class), anyInt(), nullable(SendMessageContext.class), any(DefaultMQProducerImpl.class)))
             .thenAnswer(new Answer() {