how to mock private variable in RestController class

I am doing some web unit testing with Spring. is there a way I can mock the instance of MyProcessor which get set in @PostConstruct? I tried with @MockBean but it gets set as null and getting null pointer exception?

I am using a factory to instantiate MyProcessor based on some boolean flag. But if there is a different approach altogether that would make my test cleaner, I am open to ideas.

Please Note I am using Junit 5.

public class Controller {

    private final AProcessorFactory factory;

    @Value("${tt.f.processor.async}")
    private boolean isAsync;

    private MyProcessor myProcessor;

    public Controller(final AProcessorFactory factory) {
        this.factory= factory;
    }

    @PostConstruct
    public void init() {
        myProcessor = factory.getInstance(isAsync);
    }

}


@WebMvcTest(Controller.class)
public class ControllerTest{

    @MockBean
    private MyProcessor processor;


    @MockBean
    private AProcessorFactory factory;

    @Autowired
    private MockMvc mockMvc;


    @Test
    public void test() throws Exception {           

        when(processor.process(any(Request.class), any(String.class)))
                .thenReturn(new TestResponse("123", SUCCESS, "", ""));

}

It looks like your myProcessor is actually built by your AProcessorFactory in a PostConstruct init() method.

You'll want to provide a behavior for your AProcessorFactory mock.

First, you would probably want to set up your myProcessor in your constructor as the @PostConstruct init() method has no special context loading logic with it.

public class Controller {

    @Value("${tt.f.processor.async}")
    private boolean isAsync;

    private MyProcessor myProcessor;

    public Controller(final AProcessorFactory factory) {
        this.myProcessor = factory.getInstance(isAsync);
    }
}

You can specify this in a @Before step in your test.

 @MockBean
 private AProcessorFactory factory;

 @Before
 public void setUp() {
     when(processor.process(any(Request.class), any(String.class)))
            .thenReturn(new TestResponse("123", SUCCESS, "", ""));
     when(factory.getInstance(any())).thenReturn(processor)
 }

Spring will register your AProcessorFactory mock that has been loaded with the appropriate behaviors.