Replacing a Spring bean that have Autowired dependency during testing - spring

Question

I am trying to get Spring to replace a class that has autowired dependencies with another (test class) that do not have these autowire dependencies, but I always end up with a NoSuchBeanDefinitionException like this:
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.experiments.beanreplacement.client.Connection' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true)}
I have created a simplifed example to show my problem.
I have two classes in my client package (Connection.java and TcpClient.java) and two in my application package (MessageSender.java and Scheduler.java)
package com.experiments.beanreplacement.client;
#Component
public class Connection {
public void send(String msg) { System.out.println("Connection send: " + msg); }
...
The TcpClient.java autowires the Connection class:
#Component
public class TcpClient {
#Autowired
Connection connection;
public void send(String msg) {
System.out.println("TcpClient send");
connection.send(START_OF_MESSAGE + msg + END_OF_MESSAGE);
}
}
The MessageSender class use the TcpClient to send messages:
package com.experiments.beanreplacement.application;
#Component
public class MessageSender {
#Autowired
TcpClient client;
public void sendAMessage() {
client.send("Hello world!");
client.send("Bye bye...");
}
}
I have set up a test to run this using JUnit:
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration(locations = {"/applicationContext.xml"})
public class MessageSenderTest {
#Autowired
MessageSender messageSender;
#Test
public void testMessageSender() {
messageSender.sendAMessage();
}
}
TcpClientMock class:
package client;
#Primary
public class TcpClientMock extends com.experiments.beanreplacement.client.TcpClient{
#Override
public void send(String msg) {
System.out.println("Mock client send: " + msg);
}
...
applicationContext.xml
<bean class="client.TcpClientMock" name="client" >
</bean>
<context:component-scan base-package="com.experiments.beanreplacement.application">
</context:component-scan>
...
In the applicationContext.xml file, I replace the TcpClient which is autowired in the MessageSender class with another (TcpClientMock).
I have adjusted the component-scan to only look at the path of the MessageSender and TcpClientMock, hoping to avoid having to deal with the autowire dependencies of the original TcpClient and underlying Connection.
However, I still get the "No qualifying bean of type 'com.experiments.beanreplacement.client.Connection' available: expected at least 1 bean which qualifies as autowire candidate." error even though the class using the autowire dependency is not part of the component-scan.
Is there a way to avoid this?

Answer 1

You should be able to Mock your TcpClient bean with #MockBean. In you test add:
#MockBean
TcpClient client;
in your test method you can specify the behavior of the send() method like so:
String msg = "anything";
doAnswer(i -> {
System.out.println("Mock client send: " + msg);
return null;
}
).when(client).send(msg);