对Servlet请求或响应进行JMockit测试

对Servlet请求及响应进行mock方法，

通过getMockInstance方法对servlet进行打桩，对servlet提供的方法进行mock，替代真正的servlet请求或响应。 

参考链接：

https://stackoverflow.com/questions/31689729/servlet-junit-test-using-jmockit

代码如下：

@RunWith(JMockit.class)
public class ImageServletTest3 {

     @Test
    public void testImageNotFound() throws Exception {
        ImageServlet servlet = new ImageServlet();

        servlet.doGet(
            new MockUp<HttpServletRequest>() {
              @Mock
              public String getParameter(String id){
                return null;
              }

            }.getMockInstance(),
            new MockUp<HttpServletResponse>() {
              @Mock
              public void sendError(int num){
                Assert.assertThat(num, IsEqual.equalTo(404));               
              }             
            }.getMockInstance()
       );
    }
}