code: @Override
      public WsByteBuffer buildFrameForWrite() {
  
          WsByteBuffer[] output = buildFrameArrayForWrite();
          int size = 0;
          for (WsByteBuffer b : output) {
              if (b != null) {
                  size += b.remaining();
              }
          }
          WsByteBuffer singleBuffer = this.getBuffer(size);
          singleBuffer.put(output);
          singleBuffer.flip();
          return singleBuffer;
      }
docs: The test code expects a single buffer instead of an array of buffers, as returned by buildFrameArrayForWrite