Mockito 没有从具有多个“何时”条件的模拟方法返回正确结果

Question

I have a simple DTO class:

@Data // lombok
public class MyObj {
    private int id;
    private String someProperty;
}

and a class with some computation logic for the DTO object:

public class MyClass {
    public String doSomething(MyObj obj) {
        // some calculations
    }
}

I tried to mock MyClass to use it in some unit tests, but encountered a weird problem. Therefore, I created this minimal test code to illustrate the issue:

@RunWith(MockitoJUnitRunner.class)
public class MyClassTest {
    private final MyObj myObjFirst = new MyObj();
    private final MyObj myObjSecond = new MyObj();

    @Mock
    private MyClass myClass;

    @Before
    public void setUp() {
        doReturn("OTHER")
                .when(myClass)
                .doSomething(any(MyObj.class));
        doReturn("FIRST")
                .when(myClass)
                .doSomething(myObjFirst);
        doReturn("SECOND")
                .when(myClass)
                .doSomething(myObjSecond);
    }

    @Test
    public void doSomething() {
        assertEquals("FIRST", myClass.doSomething(myObjFirst)); // fail, actual value "SECOND"
        assertEquals("SECOND", myClass.doSomething(myObjSecond));
        assertEquals("OTHER", myClass.doSomething(new MyObj()));
        assertEquals("OTHER", myClass.doSomething(new MyObj()));
    }
}

For some reason, myClass.doSomething(myObjFirst) produces the string "SECOND" instead of the expected "FIRST" , therefore the test fails at the first assert.

What am I doing wrong?

Answer 1

Solution

When stubbing, wrap the expected objects into Mockito.same to match them by reference ( see this answer for different matchers):

@Before
public void setUp() {
    doReturn("OTHER")
            .when(myClass)
            .doSomething(any(MyObj.class));
    doReturn("FIRST")
            .when(myClass)
            .doSomething(same(myObjFirst)); // <-- HERE
    doReturn("SECOND")
            .when(myClass)
            .doSomething(same(myObjSecond)); // <-- AND HERE
}

Explanation

Mockito seems to use the equals method to detect the given argument to the mocked method (reference to docs needed).

Due to Lombok's @Data annotation , a MyObj.equals implementation is generated, which compares the objects by their fields id and someProperty . Because both fields are null on myObjFirst and myObjSecond , and because last stubbing has the highest importance , Lombok first compares the argument given to myClass.doSomething against myObjSecond , immediately finding a match and returning "SECOND" .

If Lombok's @Data annotation was omitted from MyObj , the above code would work as-is, because then MyObj.equals method would default to object reference comparison, making myObjFirst not equal to myObjSecond .

In this case, however, myObjFirst equals myObjSecond equals new MyObj() , unless their properties are set to different values.