I am trying to mock a method and want to execute the internal logic as is when called. The method returns void so When I am using when(MockedObject.methodReturingVoid(any())).callRealMethod(); It gives error that the method return void. so i tried with doCallRealMethod().when(MockedObject).methodReturingVoid(any())); it give nullPointerException when as any() return null.

How can I mock this method which I want to be called with its internal logic, when the method returns void.

I am trying to mock a method and want to execute the internal logic as is when called. The method returns void so When I am using when(MockedObject.methodReturingVoid(any())).callRealMethod(); It gives error that the method return void. so i tried with doCallRealMethod().when(MockedObject).methodReturingVoid(any())); it give nullPointerException when as any() return null.

How can I mock this method which I want to be called with its internal logic, when the method returns void.

• spring-boot
• java-8
• mockito
• junit5

• This question is similar to: Mockito with void method in JUnit. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. – Ryuzaki L Commented Feb 7 at 13:23
• "I want to mock a method" and "I want to call the real method" are two contradictory statements. If you mock the method, there is no real method left to call. If you want to call the real method, why do you mock it? any() always returns null. Are you sure that MockedObject is a Mockito.mock instance? – knittl Commented Feb 7 at 13:33

1 Answer 1

Suppose you have the class you want to test:

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class SomeClass {

    public void actual() {
        log.info("Calling the actual method");
    }

    public void toMock() {
        log.warn("This should not have been invoked; mocking this one");
    }

    public void wrapper(String someArgument) {
        log.info("Calling wrapper, which invokes actual once and toMock once, argument value: {}", someArgument);
        actual();
        toMock();
    }

}

As the names suggest, actual and wrapper are to be actually invoked, while toMock will be mocked.

Then, you could write:

import org.junit.jupiter.api.Test;
import static org.mockito.Mockito.*;

class SomeClassTest {

    @Test
    void test() {
        SomeClass mock = mock(SomeClass.class);
        doCallRealMethod().when(mock).actual();
        doCallRealMethod().when(mock).wrapper(any());
        mock.wrapper("Actual argument");
        verify(mock, times(1)).actual();
        verify(mock, times(1)).toMock();
    }

}

As a brief explanation, we are setting up mockito to invoke the actual methods for actual and wrapper. We are omitting configuration for toMock.

Then we check that actual has been invoked, as well as the mock for toMock.

The code above prints:

--- [main] INFO ---SomeClass -- Calling wrapper, which invokes actual once and toMock once, argument value: Actual argument
--- [main] INFO ---SomeClass -- Calling the actual method

Edit: including formal and actual parameter.

I am using lombok and slf4j, but you can simply use System.out.println, if you prefer.