A WebClient instance allows you to handle errors (the WebClientTestImpl class) in the listMovies() method, as follows:

@Override
public Flux<Movie> listMovies() {
    return webClient.get().uri("/")
        .retrieve()
        .onStatus(HttpStatus::is4xxClientError, clientResponse ->
            Mono.error(new SampleException())
        )
        .onStatus(HttpStatus::is5xxServerError, clientResponse ->
            Mono.error(new SampleException())
        )
        .bodyToFlux(Movie.class);
}

SampleException is a custom exception class that we created by extending the Exception class. We are handling 4xx and 5xx errors, and, when encountered, it sends the custom exception as response.