@VisibleForTesting
    long getWindowSize() {
        return windowSize;
    }
@Test
    public void decodeWindowSizeFrame() throws Exception {
        final ByteBuf buffer = buildWindowSizeFrame(1234);

        while (buffer.isReadable()) {
            channel.writeInbound(buffer);
        }
        channel.finish();
        assertThat(buffer.readableBytes()).isEqualTo(0);

        assertThat((Object) channel.readInbound()).isNull();
        assertThat(decoder.getWindowSize()).isEqualTo(1234L);
    }