您如何使用 Mockito 从扩展 class 测试方法？

Question

I have a class A that extends from B. B has method called doB().

In my test, I want to return A when doB() is called.

Class B:

public String doB() {
    return "B";
}

Class A:

public class A extends B {
    
    public String doA() {
        String A = doB();
        return A;
    }
}

In my unit test, I want to do something like:

@Mock
private A a;

@Test
public void test() {
    when(a.doB()).thenReturn("PASS");
    a.doB();
    //check if it is "PASS"
}

However, it doesn't intercept when it calls doB() . Is this possible? If not, what is the best way to test this?

Answer 1

Perhaps favour composition over inheritance. In other words, instead of A extending B, A should use B. So B becomes A's collaborator.

For example:

public class B {
    public String doB() {
        return "B";
    }
}

public class A {
    private B b;

    public A(B b) {
        this.b = b;
    }

    public String doA() {
        String a = b.doB();
        return a;
    }
}

So your unit test would look something like:

public class MyTest {
    @Mock
    private B b;

    @InjectMocks
    private A a;

    @Test
    public void test() {
        when(b.doB()).thenReturn("PASS");
        a.doA();
        //check if it is "PASS"
    }
}

This is an example of how TDD can contribute to good design.

Answer 2

Since you are mocking class A, the method will not really be executed, which means there is no call to doB inside youre mock execution. you should either setup your mock to call the real method

when(a.doA()).thenCallRealMethod();
verify(a,times(1)).doB();

or use a Spy instead of a Mock.