stubbing methods that manipulates parameters with mockito

Question

I have the following situation:

class Worker {  
  public Integer somework() {  
      Integer k=0;  
      Helper h= new Helper();  
      h.change(k);  
      return k;  
    }
}

class Helper {
  public void change(Integer k) {
    //k = Some calcs
  }
}

I'm making unitests for Worker and obviously I want to mock Helper class so that his change method will always put 1 into k.

My real situation is more complicated but this code represents the issue. Thanks for help.

Answer 1

I have a method with definition like this:

class Template{
   public void process(Object rootMap, StringWriter out){
 .......   
  }
 }

I will show you how you can change/modify the "out"(StringWriter) reference.

private final Template mocktTemplate = mock(Template.class);
doAnswer(new Answer<StringWriter>() {

            public StringWriter answer(InvocationOnMock invocation)
                    throws Throwable {
                Object[] args = invocation.getArguments();
                if (args[1] instanceof StringWriter) {
                    StringWriter stringWriter = (StringWriter) args[1];
                    stringWriter.write("Email message");
                }
                return null;
            }
        }).when(this.mocktTemplate).process(anyObject(),any(StringWriter.class));

Now when you do make the actual call like:

msgBodyTemplate.process(model, msgBodyWriter);

the value of Stringbuffer ref in msgBodyWriter will be "Email message"; irrespective of it earlier value.