code: /** 
   * The big part of source's first segment is staying put. 
   */
  @Test public void writeSplitSourceBufferRight() throws Exception {
    int writeSize=Segment.SIZE / 2 - 1;
    OkBuffer sink=new OkBuffer();
    sink.writeUtf8(repeat('b',Segment.SIZE - 10));
    OkBuffer source=new OkBuffer();
    source.writeUtf8(repeat('a',Segment.SIZE * 2));
    sink.write(source,writeSize);
    assertEquals(asList(Segment.SIZE - 10,writeSize),sink.segmentSizes());
    assertEquals(asList(Segment.SIZE - writeSize,Segment.SIZE),source.segmentSizes());
  }
  