Intercept object on method invocation with Mockito

Question

I've a mocked class with a void method like

public class Mock {
    public void method(String string) {
        // doSomething
    }
}

I don't care about what this method does but I would like to get the String sent.

This String is actually an object in a JSON format, and the method that I'm testing is modifying this object depending on the String originally sent (quite random let's say).

method(String json) {
    Object obj = unparse(json);
    obj.setRandomValue(random);
    String parsed = parse(obj);
    Mock.method(parsed);
}

I would like just to see if the "randomValue", previously null, is actually set with the random after the method invocation.

The best would be to intercept the json, parse it and check the object.

Answer 1

You are looking for an ArgumentCaptor:

  Mock mock =  Mockito.mock(Mock.class);
  ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
  mock.method("input");
  Mockito.verify(mock).method(captor.capture());
  String actualValue = captor.getValue();

Answer 2

There is one more way to do this, here is example:

Mock mock =  Mockito.mock(Mock.class);
when(mock.method(any(String.class))).thenAnswer(new Answer<Void>() {

        @Override
        public Void answer(InvocationOnMock invocation) throws Throwable {
            String actualValue = invocation.getArgumentAt(0, String.class);
            Assert.assertEquals("input", actualValue);
            return null;
        }
    });
// Test your method 
mock.method("input");
Mockito.verify(mock, Mockito.times(1)).method("input");

Answer 3

Just refining answer from @softarn to match OP's example, Reference here

Mock mock =  Mockito.mock(Mock.class);
ArgumentCaptor<String> argument = ArgumentCaptor.forClass(String.class);
verify(mock).method(argument.capture());
assertEquals("{some pretty json string}", argument.getValue());