Combine #WebMcvTest with #PathVariable annotated controllers in Spring Boot 1.41 - spring-mvc

Question

Sample application for this question is here: https://github.com/olemerdy-fa/webmvctest
I am bootstrapping a new project using Spring Boot 1.4.1. I try to leverage the new features from this great framework, especially the ability to (quite-)unit test 'slices' of my application.
I am now struggled with the #WebMvcTest feature when used on a #Controller declaring a #PathVariable annotated method.
Indeed, a #WebMvcTest is supposed to bootstrap a single controller and the MockMvc testing facility, without providing anything else. Using #MockBean, it's still quite easy to provide mocks as dependencies to inject inside this controller.
But what about a #PathVariable annotated parameter whose type is, say, a JPA Entity whose converter is usually registered by Spring Data?
The sample project joined to this question contains a few samples:
MyEntity is a simple JPA entity and MyEntityRepository its Spring Data associated repository
Webmvctest1Controller has a load method retrieving the id from the path and calls itself the MyEntityRepository.findOne(id) method
Webmvctest1ControllerUnitTest tests this controller by mocking MyEntityRepository and everything just goes well
Webmvctest2Controller has a load method with a #PathVariable annotated MyEntity which is looked up by Spring Data registered converter
#RestController
public class Webmvctest2Controller {
#RequestMapping("load2/{id}")
public MyEntity load2(#PathVariable("id") MyEntity myEntity) {
return myEntity;
}
}
Webmvctest2ControllerUnitTest is where I'm stuck, as I do not know how to provide a mock entity as the parameter while still using MockMvc
#RunWith(SpringRunner.class)
#WebMvcTest(Webmvctest2Controller.class)
public class Webmvctest2ControllerUnitTest {
#Autowired
private MockMvc mvc;
#Test
public void load2() throws Exception {
// How do I mock converter to PathVariable here?
mvc.perform(get("/load2/123").accept(MediaType.APPLICATION_JSON))
.andExpect(status().isOk())
.andExpect(content().json("{id:123,name:'My Entity 123'}"));
}
}
This fails with a org.springframework.web.method.annotation.MethodArgumentConversionNotSupportedException exception
2016-10-25 14:27:55.699 WARN 20753 --- [ main] .w.s.m.s.DefaultHandlerExceptionResolver : Failed to convert request element: org.springframework.web.method.annotation.MethodArgumentConversionNotSupportedException: Failed to convert value of type [java.lang.String] to required type [com.stackoverflow.MyEntity]; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.stackoverflow.MyEntity]: no matching editors or conversion strategy found
MockHttpServletRequest:
HTTP Method = GET
Request URI = /load2/123
Parameters = {}
Headers = {Accept=[application/json]}
Handler:
Type = com.stackoverflow.Webmvctest2Controller
Method = public com.stackoverflow.MyEntity com.stackoverflow.Webmvctest2Controller.load2(com.stackoverflow.MyEntity)
Async:
Async started = false
Async result = null
Resolved Exception:
Type = org.springframework.web.method.annotation.MethodArgumentConversionNotSupportedException
ModelAndView:
View name = null
View = null
Model = null
FlashMap:
Attributes = null
MockHttpServletResponse:
Status = 500
Error message = null
Headers = {}
Content type = null
Body =
Forwarded URL = null
Redirected URL = null
Cookies = []
Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.375 sec <<< FAILURE! - in com.stackoverflow.Webmvctest2ControllerUnitTest
load2(com.stackoverflow.Webmvctest2ControllerUnitTest) Time elapsed: 0.015 sec <<< FAILURE!
java.lang.AssertionError: Status expected:<200> but was:<500>
at org.springframework.test.util.AssertionErrors.fail(AssertionErrors.java:54)
at org.springframework.test.util.AssertionErrors.assertEquals(AssertionErrors.java:81)
at org.springframework.test.web.servlet.result.StatusResultMatchers$10.match(StatusResultMatchers.java:664)
at org.springframework.test.web.servlet.MockMvc$1.andExpect(MockMvc.java:171)
at com.stackoverflow.Webmvctest2ControllerUnitTest.load2(Webmvctest2ControllerUnitTest.java:28)
WebmvctestApplicationTests shows that everything is fine in both cases when the application is fully bootstrapped
Any idea of how I could keep my #PathVariable entity parameters while still only testing my web slice with #WebMvcTest?
Thanks :)

Answer 1

Thanks to #zeroflagL hinting about possible contributions to HandlerMethodArgumentResolver, I've come up with a solution that seems to fit my need. Contributing a custom Converter handling the mock entity injection in the controller seems to do the job
#RunWith(SpringRunner.class)
#WebMvcTest(Webmvctest2Controller.class)
public class Webmvctest2ControllerUnitTest {
#Autowired
private MockMvc mvc;
#Test
public void load2() throws Exception {
mvc.perform(get("/load2/123").accept(MediaType.APPLICATION_JSON))
.andExpect(status().isOk())
.andExpect(content().json("{id:123,name:'My Entity'}"));
}
#TestConfiguration
static class InternalConfig {
#Bean
WebMvcConfigurer configurer() {
return new WebMvcConfigurerAdapter() {
#Override
public void addFormatters(FormatterRegistry registry) {
registry.addConverter(String.class, MyEntity.class, id -> {
if (id.equals("123")) {
MyEntity myEntity = new MyEntity(123);
myEntity.setName("My Entity");
return myEntity;
}
throw new IllegalArgumentException();
});
}
};
}
}
}
It is not perfect, as the mock Entity cannot be provided by the test method itself but it is still allows the web-unit-test bootstrap and run I wanted to keep.