mockito return value based on property of a parameter

Question

Normally when using mockito I will do something like

Mockito.when(myObject.myFunction(myParameter)).thenReturn(myResult);

Is it possible to do

Answer 1

You can do this with Mockito 3.6.0:

when(mockObject.myMethod(anyString()))
    .thenAnswer(invocation -> myStringMethod(invocation.getArgument(0)));

This answer is based on Sven's answer and Martijn Hiemstra's comment, with getArgumentAt() changed to getArgument().

Answer 2

Here's one way of doing it. This uses an Answer object to check the value of the property.

@RunWith(MockitoJUnitRunner.class)
public class MyTestClass {
    private String theProperty;
    @Mock private MyClass mockObject;

    @Before
    public void setUp() {
        when(mockObject.myMethod(anyString())).thenAnswer(
            new Answer<String>(){
            @Override
            public String answer(InvocationOnMock invocation){
                if ("value".equals(theProperty)){
                    return "result";
                }
                else if("otherValue".equals(theProperty)) {
                    return "otherResult";
                }
                return theProperty;
            }});
    }
}

There's an alternative syntax, which I actually prefer, which will achieve exactly the same thing. Over to you which one of these you choose. This is just the setUp method - the rest of the test class should be the same as above.

@Before
public void setUp() {
    doAnswer(new Answer<String>(){
        @Override
        public String answer(InvocationOnMock invocation){
            if ("value".equals(theProperty)){
                return "result";
            }
            else if("otherValue".equals(theProperty)) {
                return "otherResult";
            }
            return theProperty;
        }}).when(mockObject).myMethod(anyString());
}

Answer 3

In Java 8 it is even simpler than all of the above:

when(mockObject.myMethod(anyString()))
    .thenAnswer(invocation -> 
        invocation.getArgumentAt(0, String.class));

Answer 4

Here is how it would look like in Kotlin with mockito-kotlin library.

mock<Resources> {
    on {
        mockObject.myMethod(any())
    } doAnswer {
        "Here is the value: ${it.arguments[0]}"
    }
}

Answer 5

Yes you can, using a custom argument matcher.

See the javadoc of Matchers for more details, and more specifically ArgumentMatcher.