import org.jmock.Mockery; import org.jmock.Expectations; Mockery context = new Mockery(); final MyInterface mockObject = context.mock(MyInterface.class); context.checking(new Expectations() {{ oneOf(mockObject).methodName(with(any(String.class))); will(returnValue("Mocked Result")); }}); String result = mockObject.methodName("input"); context.assertIsSatisfied();