Mocking method behaviour based on the field of the parameter Java 8

Question

I have a class definition as follows:

public class MyClass {

    public performExecution(ParamsClass paramsClassObject);
}

public ParamsClass {
    private String field1;
    private String field2;
}

Now, I want to mock the method performExecution based on the field1, but there is no direct way to do it even with the ArgumentMatchers.

Suppose I mocked the class:

MyClass myClass = mock(MyClass.class)

Now, I want to perform something like this: when the Params object passed in myClass.performExecution() has the field1 value as "1", then give a certain response, otherwise some other response.

Is that a way to do that ?

Answer 1

There are a couple of options:

Option 1: Custom argument matcher

See for example Custom Argument Matcher by baeldung

Option 2: when / thenAnswer

@Test
void testThenAnswer() {
    MyClass myCollaborator = Mockito.mock(MyClass.class);
    when(myCollaborator.performExecution(any(ParamsClass.class)))
            .thenAnswer((invocationOnMock -> {
        ParamsClass params = invocationOnMock.getArgument(0);
        return "f1".equals(params.getField1())
                ? "V1"
                : "V2";
    }));

    var result = myCollaborator.performExecution(new ParamsClass("f1", "f2"));
    Assertions.assertThat(result).isEqualTo("V1");
}

Option 3: argThat Matcher

@Test
void testArgThat() {
    MyClass myCollaborator = Mockito.mock(MyClass.class);
    when(myCollaborator.performExecution(Mockito.argThat(p -> p != null && "f1".equals(p.getField1())))).thenReturn("V1");
    when(myCollaborator.performExecution(Mockito.argThat(p -> p != null && !"f1".equals(p.getField1())))).thenReturn("V2");

    var result = myCollaborator.performExecution(new ParamsClass("f1", "f2"));
    Assertions.assertThat(result).isEqualTo("V1");
}

Note null checks in argThat matchers