Mockito return value based on property of a parameter

Normally when using Mockito I will do something like:

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

Is it possible to do something along the lines of

myParameter.setProperty("value");
Mockito.when(myObject.myFunction(myParameter)).thenReturn("myResult");

myParameter.setProperty("otherValue");
Mockito.when(myObject.myFunction(myParameter)).thenReturn("otherResult");

So rather than when just using the parameter to determine the result. It is using a value of a property inside the parameter to determine the result.

So when the code is executed it behaves like so:

public void myTestMethod(MyParameter myParameter,MyObject myObject){
    myParameter.setProperty("value");
    System.out.println(myObject.myFunction(myParameter));// outputs myResult

    myParameter.setProperty("otherValue");
    System.out.println(myObject.myFunction(myParameter));// outputs otherResult
}

---

Here is the current solution, hopefully something better can be suggested.

private class MyObjectMatcher extends ArgumentMatcher<MyObject> {

    private final String compareValue;

    public ApplicationContextMatcher(String compareValue) {
        this.compareValue= compareValue;
    }

    @Override
    public boolean matches(Object argument) {
        MyObject item= (MyObject) argument;
        if(compareValue!= null){
            if (item != null) {
                return compareValue.equals(item.getMyParameter());
            }
        }else {
            return item == null || item.getMyParameter() == null;
        }
        return false;
    }
}

public void initMock(MyObject myObject){
    MyObjectMatcher valueMatcher = new MyObjectMatcher("value");
    MyObjectMatcher otherValueMatcher = new MyObjectMatcher("otherValue");
    Mockito.when(myObject.myFunction(Matchers.argThat(valueMatcher))).thenReturn("myResult");
    Mockito.when(myObject.myFunction(Matchers.argThat(otherValueMatcher))).thenReturn("otherResult");
}

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

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

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());
}

Yes you can, using a custom argument matcher.

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

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]}"
    }
}

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().