@Test
    void webSocketFails() {
        final Server server = Server.builder().service("/", (ctx, req) -> HttpResponse.of(200)).build();
        server.start().join();
        final WebSocketClient webSocketClient = WebSocketClient.of(
                "h1c://127.0.0.1:" + server.activePort().localAddress().getPort());
        final CompletableFuture<WebSocketSession> future = webSocketClient.connect(
                "/", HttpHeaders.of(HttpHeaderNames.EXPECT, HttpHeaderValues.CONTINUE.toString()));
        assertThatThrownBy(future::join)
                .hasCauseInstanceOf(UnprocessedRequestException.class)
                .cause()
                .hasCauseInstanceOf(IllegalArgumentException.class)
                .hasMessageContaining("a WebSocket request is not allowed to have Expect: 100-continue header");
        server.stop().join();
    }
This test is to check the behavior of the HttpClient when the 'Expect: 100-continue' header is set.
core/src/test/java/com/linecorp/armeria/client/HttpClientExpect100HeaderTest.java