@Test
    void testEmptyClientFactoryOptions() throws Exception {
        final ClientFactory clientFactory = ClientFactory.builder()
                                                         .options(ClientFactoryOptions.of(ImmutableList.of()))
                                                         .build();
        final BlockingWebClient client = WebClient.builder(server.httpUri())
                                                  .factory(clientFactory)
                                                  .build()
                                                  .blocking();

        final AggregatedHttpResponse response = client.execute(
                AggregatedHttpRequest.of(HttpMethod.GET, "/hello/world"));
        assertThat(response.status()).isEqualTo(HttpStatus.OK);

        clientFactory.closeAsync();
    }
User-agent header should be overridden by ClientOption.HTTP_HEADER
core/src/test/java/com/linecorp/armeria/client/HttpClientIntegrationTest.java