Creating and asserting a mocked interface with MockFor

ThemeWriterTest.groovy

        def expected = "text/plain";
        mock  = new MockFor( HttpServletResponse.class );
        mock.demand.with {
            setContentType{ String got -> assert expected == got }
        }
        def mockHttpServletResponse = mock.proxyInstance();
        def themeWriter = new ThemeWriter( mockHttpServletResponse );
        themeWriter.generateResponse();
        mock.verify( mockHttpServletResponse );