@Test
        void http1SendsOneHostHeaderWhenUserSetsIt() {
            final BlockingWebClient client = BlockingWebClient.of(
                    "h1c://localhost:" + ((ServerConnector) jetty.getConnectors()[0]).getLocalPort() + '/');

            final AggregatedHttpResponse response = client.execute(
                    RequestHeaders.of(HttpMethod.GET, "/onlyonehost", HttpHeaderNames.HOST, "foobar")
            );
            assertThat(response.status()).isEqualTo(HttpStatus.OK);
        }
User-agent header should be overridden by ClientOption.HTTP_HEADER
core/src/test/java/com/linecorp/armeria/client/HttpClientIntegrationTest.java