Spring MVC: How to unit test Model's attribute from a controller method that returns String?

Question

For example,

package com.spring.app;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

/**
 * Handles requests for the application home page.
 */
@Controller
public class HomeController {
    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String home(final Model model) {
        model.addAttribute("msg", "SUCCESS");
        return "hello";
    }

}

I want to test model 's attribute and its value from home() using JUnit. I can change return type to ModelAndView to make it possible, but I'd like to use String because it is simpler. It's not must though.

Is there anyway to check model without changing home() 's return type? Or it can't be helped?

Answer 1

You can use Spring MVC Test :

mockMvc.perform(get("/"))
                .andExpect(status().isOk())
                .andExpect(model().attribute("msg", equalTo("SUCCESS"))) //or your condition

And here is fully illustrated example

Answer 2

I tried using side effect to answer the question.

@Test
public void testHome() throws Exception {
    final Model model = new ExtendedModelMap();
    assertThat(controller.home(model), is("hello"));
    assertThat((String) model.asMap().get("msg"), is("SUCCESS"));
}

But I'm still not very confident about this. If this answer has some flaws, please leave some comments to improve/depreciate this answer.

Answer 3

You can use Mockito for that.

Example:

@RunWith(MockitoJUnitRunner.class) 
public HomeControllerTest {

    private HomeController homeController;
    @Mock
    private Model model;

    @Before
    public void before(){
        homeController = new HomeController();
    }

    public void testSomething(){
        String returnValue = homeController.home(model);
        verify(model, times(1)).addAttribute("msg", "SUCCESS");
        assertEquals("hello", returnValue);
    }

}