Mock a nested class with constructor parameters and test the methods

Question

I am trying to Mock a class which has a nested class. That nested class was with a constructor argument. When I am trying to test using mockito instead of mocking the actual method is getting executed.

I have done @InjectMocks on outer class and @Mock of the inner class.

//Actual Class to test using Mockito.

public class ClassA {

public void initMethod(String s1, String s2, String s3, String s4) throws Exception {

    ClassB objB = null;
    if (objB == null && s3 != null && s4 != null && s2 != null) {

        SampleUtil.KeyStorePasswordPair pair = SampleUtil.getKeyStorePasswordPair(s3, s4);


        objB = new ClassB(s1, s2, pair.keyStore, pair.keyPassword);

        try {
            objB.meth1();  //Note: meth1 and meth2 are void methods.  
            objB.meth2();  // These two methods only to be accessed. something like doNothing

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
}

Which I have tried as usual to call the class using @Mock but the actual method meth1() is getting accessed.

//Somthing which I tried 
@RunWith(MockitoJUnitRunner.class)
public class MockitoTest {


@InjectMocks
ClassA classA;

@Mock
ClassB classB;

@Before
public void initMocks() {
    MockitoAnnotations.initMocks(this);
}

@Test
public void testInitClient() throws Exception {
    // Setup

    // Run the test
    classA.initMethod("Lorem", "Ipsum", "TestStr1", "TestStr2");

    doNothing().when(classB).meth1(); // This is the line need to be mocked. But instead calling the actual method and executing
    // Verify the results
}

The inner ClassB method needs to be mocked instead of accessing the real method.

As a beginner to mockito I am trying to clear this. But got confused on few points like accessing void method, SO can't use when then. Accessing constructor with parameter etc.,

Paul Cosma Paul Cosma · Accepted Answer · 2019-04-15T20:11:57

I don't think this is possible without some kind of dependency injection.

Here, I modified your code so that it behaves as you wanted.

public class ClassA {
    // Needed so that it can be replaced with setter
    private ClassB objB;

    // Extract the generation of ClassB so that it can be prevented
    public void generateClassB(String s1, String s2) {
        this.objB = new ClassB(s1, s2);
    }

    public void initMethod(String s1, String s2, String s3, String s4) {

        objB = null;
        if (s3 != null && s4 != null && s2 != null) {

            SampleUtil.KeyStorePasswordPair pair = SampleUtil.getKeyStorePasswordPair(s3, s4);

            generateClassB(s1, s2);

            try {
                objB.meth1();  //Note: meth1 and meth2 are void methods.
                objB.meth2();  // These two methods only to be accessed. something like doNothing

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public void setClassB(ClassB classB) {
        this.objB = classB;
    }
}

This is the implementation of ClassB that I used in order to test the results.

public class ClassB {
    private String s1;
    private String s2;

    public ClassB(String s1, String s2) {
        this.s1 = s1;
        this.s2 = s2;
    }

    public void meth1() {
        System.out.println(s1);
    }

    public void meth2() {
        System.out.println(s2);
    }
}

And the test file

@RunWith(MockitoJUnitRunner.class)
public class DemoApplicationTests {
    private ClassA classA;
    private ClassB classB;

    @Test
    public void testInitClient() {
        classA = Mockito.spy(ClassA.class);
        classB = Mockito.spy(new ClassB("a", "b"));

        Mockito.doNothing()
                .when(classB)
                .meth1();

        // This will replace the ClassA#generateClassB method call with the setter
        Mockito.doAnswer(args -> {
            classA.setClassB(classB);
            return null;
        }).when(classA).generateClassB(Mockito.any(), Mockito.any());
        classA.initMethod("a", "b", "c", "d");
    }
}

An alternative, and much cleaner, solution would be to pass ClassB instance to ClassA#initMethod.

Mock a nested class with constructor parameters and test the methods

1 Answers