Spring webflux, testing `ServerResponse` - spring

Question

How can I test a handler method that receive ServerRequest and return Mono<ServerResponse> ?
I can create a ServerRequest via org.springframework.mock.web.reactive.function.server.MockServerRequest.builder(). And assert on the ServerResponse.statusCode(). However I would like to test the body of this ServerResponse but there is no way to extract it.
ServerResponse response = target.search(MockServerRequest.builder()
.method(HttpMethod.GET)
.build()
).block();
assertThat(response.statusCode()).isEqualTo(HttpStatus.OK);
//assertThat(response.body()).isNotNull();
I don't want to do a broader test with the WebTestClient, I would like to test all possible cases of response with unit tests.
Thanks

Answer 1

So, it seems that the best solution is to use the WebTestClient. However this one can be used without a running server;
The spring-test module includes a WebTestClient that can be used to test WebFlux server endpoints with or without a running server.
-- https://docs.spring.io/spring/docs/5.0.0.BUILD-SNAPSHOT/spring-framework-reference/html/web-reactive.html#web-reactive-tests
The trick is to use the bindTo..() builder method. In my case bindToRouterFunction(new MyRouter(new MyHandler())) works well

Answer 2

I had exactly the same question, because I don't want to start the entire Spring context for every test. Thanks for the info in the own-answer, this helped me. Here is a complete example including Mockito and JUnit5:
import java.util.Arrays;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;
import org.springframework.http.MediaType;
import org.springframework.test.web.reactive.server.WebTestClient;
#ExtendWith(MockitoExtension.class)
class UsersHandlerTest {
#Mock
UserRepository userRepository;
WebTestClient client;
#BeforeEach
public void setUp() {
UsersHandler usersHandler = new UsersHandler(userRepository);
Router router = new Router(usersHandler);
Mockito.when(userRepository.findAll()).thenReturn(
Arrays.asList("", ""));
client = WebTestClient.bindToRouterFunction(router.getUsers()).build();
}
#Test
public void getCommands() {
client.get().uri("/users")
.accept(MediaType.APPLICATION_JSON_UTF8)
.exchange()
.expectStatus().isOk()
.expectBody().json("{}");
}
}

Answer 3

I have asked a similar question insisting not to use WebTestClient.
I have ended up answering my own question after discovering that it is possible to cast the response to a type that allows inspecting body (entity).
The magic line (Kotlin) is:
(serverResponse as EntityResponse<Fleet>).entity()
Edit:
So for the case of expecting an empty body, you could do:
assert(serverResponse !is EntityResponse<*>)
Thanks for #andred for pointing this out