public WebClient webClient() {
        final WebClient webClient = this.webClient.get();
        if (webClient != null) {
            return webClient;
        }

        final WebClient newWebClient = webClientBuilder().build();
        if (this.webClient.compareAndSet(null, newWebClient)) {
            return newWebClient;
        } else {
            final WebClient oldWebClient = this.webClient.get();
            assert oldWebClient != null;
            return oldWebClient;
        }
    }
Returns the {@link WebClient} configured by {@link #configureWebClient(WebClientBuilder)}.
junit5/src/main/java/com/linecorp/armeria/internal/testing/ServerRuleDelegate.java