final SockJsConfig config = SockJsConfig.withPrefix("/echo").build();
final EmbeddedChannel ch = webSocketChannel(config);
final FullHttpRequest request = new DefaultFullHttpRequest(HTTP_1_1, GET, "/websocket");
request.retain();
ch.writeInbound(request);
final FullHttpResponse response = decodeFullHttpResponse(ch);
assertThat(response.getStatus(), is(BAD_REQUEST));
assertThat(response.headers().get(CONTENT_TYPE), is(Transports.CONTENT_TYPE_PLAIN));
assertThat(response.content().toString(CharsetUtil.UTF_8), equalTo("Can \"Upgrade\" only to \"WebSocket\"."));
}