Making a mocked method return an argument that was passed to it

Question

Consider a method signature like:

public String myFunction(String abc);

Can Mockito help return the same string that the method received?

Answer 1

You can create an Answer in Mockito. Let's assume, we have an interface named Application with a method myFunction.

public interface Application {
  public String myFunction(String abc);
}

Here is the test method with a Mockito answer:

public void testMyFunction() throws Exception {
  Application mock = mock(Application.class);
  when(mock.myFunction(anyString())).thenAnswer(new Answer<String>() {
    @Override
    public String answer(InvocationOnMock invocation) throws Throwable {
      Object[] args = invocation.getArguments();
      return (String) args[0];
    }
  });

  assertEquals("someString",mock.myFunction("someString"));
  assertEquals("anotherString",mock.myFunction("anotherString"));
}

Since Mockito 1.9.5 and Java 8, you can also use a lambda expression:

when(myMock.myFunction(anyString())).thenAnswer(i -> i.getArguments()[0]);