Mockito when() method not working and getting null pointer exception

Question

I am writing unit test cases using Mockito and JUnit . But getting NullPointerException when running a test. On debugging I get to know that Mockito on method: when().thenReturn() is not returning a value for dependent methods and the calling program is calling those methods to get result.

Below is my dummy code to get idea of structure of code:

class B {
  public C getValue() {
    return C;
  }
}

class A {
  public D getAns(String q1, String q2) {
    return B.getValue().map(mapper::toD); //null pointer exception start here 
  } 
}

@RunWith(MockitoJunitrunner.test)
class TestA {
  
  @InjectMock
  A a;

  @Mock
  B b;
  C c;

  init() {
    when(b.getValue()).thenReturn(c);
  }

  @Test
  public void getA() {
    D ans=A.getAns(q1,q2);  //getting null pointer exception here 
    AssertNotNull(ans);
  }
}

There is nothing to inject into A and looks like getValue() is a static method. If that isn't the case please add code that represents your case. — M. Deinum
– M. Deinum, Commented Aug 26, 2020 at 5:58
getValue() is not static . and my code is exactly like above code — Sam
– Sam, Commented Aug 26, 2020 at 6:07

Vishwa Ratna · Accepted Answer · 2020-08-26 06:37:28Z

1

You have classes calling each others methods so it is better to use Mockito.RETURNS_DEEP_STUBS

In your Case:

A is calling B and B is calling C

Just replace:

 @InjectMock
  A a;

  @Mock
  B b;
  C c;

With :

A a = Mockito.mock(A.class, Mockito.RETURNS_DEEP_STUBS);
B b = Mockito.mock(B.class, Mockito.RETURNS_DEEP_STUBS);
C c = Mockito.mock(C.class, Mockito.RETURNS_DEEP_STUBS);

edited Aug 26, 2020 at 6:37

answered Aug 26, 2020 at 6:20

Vishwa Ratna

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2 Comments

Sam Over a year ago

A is calling B and B is calling C

Vishwa Ratna Over a year ago

@SakshiMishra then use A a = Mockito.mock(A.class, Mockito.RETURNS_DEEP_STUBS); B b = Mockito.mock(B.class, Mockito.RETURNS_DEEP_STUBS); instead of simple mock. Try it and let me know if you still get NPE ??

Soni · Accepted Answer · 2020-08-26 05:59:55Z

1

There may be multiple reason to why when(...).thenReturn(...) is not called :

The data type which is used in when construct is not matching exact, for example, if you have a string and you pass null, its not same method call
Ensure that the objects are getting initialized using the same approach. A spring injected resource is not same as the one created using new operator

answered Aug 26, 2020 at 5:59

Soni

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1 Comment

Derek Over a year ago

This helped me track down my issue - with the combination of non-matching arguments and RETURNS_DEEP_STUBS, mockito was returning mocked stubs instead of what I was intending it to. Thanks!

Sam · Accepted Answer · 2022-05-06 19:05:05Z

0

use @InjectMock and @Mock to solve this issue

answered May 6, 2022 at 19:05

Sam

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1 Comment

Community Over a year ago

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