We use Wiremock to test Client functionality. It can be done in standard unit test or a SpringBoot test.

Below code explains the Unit testing in regular tests.

@Service
class MoviesClient {
  private final WebClient moviesWebClient;

  public Mono<Movie> findMovieById(String movieID) {
    return moviesWebClient.get().uri(MOVIE_ENDPOINT+"/"+movieID).bodyValue(job).retrieve()
        .bodyToMono(Movie.class);
  }
}

Now as we see MoviesClient needs webClient to call the movie service and get movie.

  @ExtendWith({MockitoExtension.class})
    class MoviesClientTest {
    
        private MoviesClient moviesClient;
        
        @RegisterExtension
          private static final WireMockExtension MOVIES_WM =
         WireMockExtension.newInstance().options(wireMockConfig().port("8086")).build();
        
        @BeforeEach
        void setup() {
        
        var webClient = WebClient.builder().baseUrl("http://localhost:8086")
                .defaultHeader(CONTENT_TYPE, APPLICATION_JSON_VALUE).build();
        moviesClient = new MoviesClient(moviesClient)
MOVIES_WM.stubFor(get(MOVIE_ENDPOINT+"/"+"1234")).withHeader(CONTENT_TYPE, matching(APPLICATION_JSON_VALUE))willReturn(aResponse().withStatus(OK.value()).withHeader(CONTENT_TYPE, APPLICATION_JSON_VALUE)
            .withBody("Your json response body comes here")));
        }
}

Now you can write your tests to call the method on client which in turn will make a webclient call which will be stubbed to wiremock server.

@Test
void testMoviesEndPoint() {
  StepVerifier.create(moviesClient.findMovieById(1234)
  .expectNext(movie -> assertThat(movie).getId.equals(1234))
  .verifyComplete();

FLUENT_WM.verify(1, postRequestedFor(urlEqualTo(MOVIE_ENDPOINT+"/"+"1234")));
}