27 July 2013

404 error with spring mvc testing

We have a standard rest application built with spring mvc (v3.2.3). Let's add another controller (MyController) with one method that does some computations and returns an empty response with 200 OK. Test first:
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

import org.junit.*;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;

public class MyControllerTest {

 private MockMvc mockMvc;

 @Test
 public void test() throws Exception {
  mockMvc.perform(get("/my/test"))

   .andExpect(status().isOk())
   .andExpect(content().string(""));
 }

 @Before
 public void setUp() throws Exception {
  mockMvc = MockMvcBuilders.standaloneSetup(new MyController()).build();
 }
}
Nothing new, everything just as in spring's tutorial. So now let's write the code:
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class MyController {

 @RequestMapping("/my/test")
 public void test() {
  System.out.println("test method executed"); //yes, yes, I know
 }
}
Test is green, that was easy. Let's see our code in action. Start jetty and check the address /my/test. Method is executed and we get... 404 not found. Wtf?!

Probably the quickest way to find the problem is to compare the method with other working controllers. Of course, I forgot about @ResponseBody. After adding it, jetty displays the page correctly and test still passes. But the purpose of writing tests is to have protection against such mistakes. So why the test was green?

For void methods without @ResponseBody spring forwards request processing to DispatcherServlet which, in this case, fails trying to resolve a view for the specified url. But for some reason mockMvc reports empty response and status 200. I reported it as a bug but it got status 'Works as Designed'. So how can we eliminate the false positive? We need to explicitly check if no forwarding is done. And there is an existing ResultMatcher for this:
forwardedUrl(null)
It can be added with another andExpect inside each test. But turning it on globally will save you from such mistakes in future:
@Before
public void setUp() throws Exception {
 mockMvc = MockMvcBuilders.standaloneSetup(new MyController())
                             .alwaysExpect(forwardedUrl(null))
                             .build();
}
After adding this matcher, the test without @ResponseBody fails:
java.lang.AssertionError: Forwarded URL expected:<null> but was:<my/test>

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