Spring webflux, testing `ServerResponse`

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

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("{}");  }}

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