Can we mock the instance if it declared with new key word that is inside the method we are testing? - spring-boot

Question

I'm new to Mockito and Junit, I'm working with Spring Boot
I want to know that can we mock the instance if it declared with a new keyword that is inside the method we are testing?
For example:
#Service
class A {
#Autowired
X x;
#Autowired
Y y;
public void testMe(){
imCommunicatingWithSomeRestClient();
}
private void imCommunicatingWithSomeRestClient(){
String body="";
MyRestClient client=new MyRestClient(iTakeUrlNeedsToHit); //no arg constructor not exist and suppose this is the method of some Core jar project
client.callDataRest(HTTP.GET,body)
}
}
Although I wanted to mock it, I've tried all #Spy #Mock, #InjectMocks to check if it'll behave differently but none of these worked for me as it always creates a new object and calls the real method.
So I change approach slightly and did it with using BeanFactory and instead of new I replace that with :
MyRestClient client=beanFactory.getBean(MyRestClient.class,jobDataRestUrl);
so I have these questions:
Already asked above (if we mock the instance if it declared with new keyword that is inside the method we are testing).
If my current project is Spring Boot project and MyRestClient is inside the jar written in the core. Is the standard say I should not create it by Bean Factory because I think I should do it by that way and let the Spring handles that
I even tried with reflection but it seems it is also not working with the instance created with new keyword inside a method and not on the class level.

Answer 1

Your current setting is not efficiently testable. You may still do it with lots of weird workarounds, but still, not recommended. Here's what you can do; firstly, you should not have any kind of dependency initialization inside your classes (like new MyRestClient(...)). So, move the REST client to the property level and have it injected through constructor.
#Service
class A {
private final X x;
private final Y y;
private final MyRestClient restClient;
public A (X x, Y y, MyRestClient restClient) {
this.x = x;
this.y = y;
this.restClient = restClient;
}
public void testMe() {
imCommunicatingWithSomeRestClient();
}
private void imCommunicatingWithSomeRestClient() {
String body = "";
restClient.callDataRest(GET, body);
}
}
Since you are using Spring, you can create a bean of the REST client and move the endpoint URL to an external property.
class Config {
#Bean
public MyRestClient myRestClient(#Value("${property.name}") String url) {
return new MyRestClient(url);
}
}
Finally, you can easily mock the behavior of that REST client.
#ExtendWith(MockitoExtension.class)
class TestA {
#Mock
private X x;
#Mock
private Y y;
#Mock
private MyRestClient restClient;
#InjectMocks
private A a;
// your tests...
}