private static void sendEmptySettingsAndAckFrame(BufferedOutputStream bos) throws IOException {
        // Send an empty SETTINGS frame.
        bos.write(new byte[] { 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00 });
        // Send a SETTINGS_ACK frame.
        bos.write(new byte[] { 0x00, 0x00, 0x00, 0x04, 0x01, 0x00, 0x00, 0x00, 0x00 });
        bos.flush();
    }
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