EasyMock (http://easymock.org/) is a mocking framework. To use it with Testify, you simply create mocks in the doSetUp() method of your test classes.
public class MyTest extends AbstractMyApplicationTest {
@ForComponents MyService service;
public void doSetUp() {
service = EasyMock.createMock(MyService.class);
}
public void testElementIsOnPage() {
expect(service.shouldShowElement()).andReturn(true);
replay(service);
Document page = tester.renderPage("mypage");
assertNotNull(page.getElementById("myid"));
}