Programmatically instantiate a FeignClient for tests - spring-cloud-netflix

Question

I have a dead simple FeignClient interface that I would like to "unit"/integration test with a fake HTTP server, WireMock for example. The idea is to test the mapping with a sampled HTTP API response, without configuring a whole Spring Boot/Cloud Context.
#FeignClient(name = "foo", url = "${foo.url}")
public interface FooClient {
#RequestMapping(value = "/foo/{foo-id}/bar", method = RequestMethod.GET)
public Bar getBar(#PathVariable("foo-id") String fooId);
}
Is there any way to programmatically instantiate this interface, like a Spring Data Repository through a *RepositoryFactoryBean ?
I see a FeignClientFactoryBean in the source code, but it is package protected, and it relies on an ApplicationContext object to retrieve its dependencies anyway.

Answer 1

Well, you can fake a real rest client using wiremock for testing purposes, but this is more about containing the functional test, that feign clients themself work. This is mostly not what you really want to test, because the actual need is to test your components using your client behave in a specified way.
The best practice for me is not to make live hard with maintaing a fake server, but mock the clients behavior with Mockito. If you use Spring Boot 1.4.0, here is the way to go:
Consider you have some FooBarService, which internally uses your FooClient to peform some FooBarService::someAction(String fooId), which performs some business logic which needs to work with a foo with given id
#RunWith(SpringRunner.class)
#SpringBootTest(classes = App.class)
class FooUnitTest {
#Autowired;
private FooBarService fooBarService;
#MockBean;
private FooClient fooClient;
#Test
public void testService() {
given(fooClient.getBar("1")).willReturn(new Bar(...));
fooBarService.someAction("1");
//assert here, that someAction did what it supposed to do for that bar
}
}
At this point you first should clarify, what you expect the REST client to respond, when asking for "/foo/1/bar", by creating a mock for exactly that case and give the Bar object you expect to receive for that API, and assert that your application is in the desired state.