How to mock method call and return value without running the method?

Question

Consider the following method:

public boolean isACertainValue() {
        if(context.getValueA() != null && context.getValueA().toBoolean() == true) {
        if(context.getType() != null && context.getType() == ContextType.certainType) {
            return true;
        }
    }
    return false;
}

I did not write this code, it is ugly as hell, it is totally overcomplicated but I have to work with it.

Now I want to test a method that relies on a call to this method.

I thought I could deal with this by:

Mockito.when(spy.isACertainValue()).thenReturn(true); because that's the case I want to test.

But it doesn't work as it is still calling the method-body :/

I get nullpointers or rather I get something along the lines of

misusing.WrongTypeOfReturnValue; Boolean cannot be returned by getValueA(). getValueA() should return ValueA

So I tried (as a workaround) to do:

Mockito.when(contextMock.getValueA()).thenReturn(new ValueA()); and Mockito.when(contextMock.getType()).thenReturn(ContextType.certainType);

but then I get a nullpointer that I cant seem to be able to debug.

So, how is it done right in this case?

That is exactly how to do it, but maybe there is a value IN that valueA you need further on in your test, so you should also mock the object returned, not just return an instance instantiated with a (default) constructor. — Stultuske, Dec 16 '15 at 10:01
I had similar problem (a method in a super class was not mocked). The conclusion was that it was a bug in Mockito. Updating Mockito to 2.28.2 helped. — Arkadiusz Cieśliński, Jul 26 '19 at 12:35

Tunaki · Accepted Answer · 2017-05-02T13:25:28.697

39

When you are invoking

Mockito.when(spy.isCertainValue()).thenReturn(true);

the method isCertainValue() is getting called here. This is how Java works: to evaluate the argument of Mockito.when, the result of spy.isCertainValue() must be evaluated so the method must be called.

If you don't want that to happen, you can use the following construct:

Mockito.doReturn(true).when(spy).isCertainValue();

This will have the same mocking effect but the method won't be called with this.

edited May 02 '17 at 13:25

answered Dec 16 '15 at 10:02

Tunaki

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1

Thank you, I'm more on track now... I get a nullpointer tho xD I hate this program so much, it's an abomination :X – Dec 16 '15 at 10:04
Broken link. Where do you setup spy? – powder366 May 02 '17 at 13:18
1

It worked for me. It stopped throwing NPE. Thanks Tunaki! – coretechie Aug 09 '17 at 11:44
Do I have to run with **MockitoJUnitRunner** for this to work? – IgorGanapolsky Aug 14 '17 at 16:16
Imagine we have a aspect on this method. Then the aspect will be evaluated anyway. Do you have an idea how to bypass the aspect call ? – voipp Nov 07 '18 at 17:51
3

Doesn't work for me - Argument passed to when() is not a mock! – skryvets Jun 25 '19 at 19:15
@skryvets just in case it isn't obvious: it seems that you're most likely passing in the real object and not a Spy/Mock of that object. Cheers! – Fearnbuster Aug 16 '23 at 21:07

score 1 · Answer 2 · answered Jan 30 '17 at 15:53

This code is correct:

Mockito.when(contextMock.getType()).thenReturn(ContextType.certainType);

But you are getting NullPointerException because you didn't define the Mocking value that should be defines, well I'm using Spring, in my context file when I define @Autowired bean I define it this way:

<bean id="contextMock" class="org.mockito.Mockito" factory-method="mock">
    <constructor-arg value="com.example.myspringproject.bean.ContextMock" />
</bean>

How to mock method call and return value without running the method?

2 Answers2

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