code: @Test public void testExpandAppend() throws Exception {
    CharArrayBuffer buffer=new CharArrayBuffer(4);
    Assert.assertEquals(4,buffer.capacity());
    char[] tmp=new char[]{'1','2','3','4'};
    buffer.append(tmp,0,2);
    buffer.append(tmp,0,4);
    buffer.append(tmp,0,0);
    Assert.assertEquals(8,buffer.capacity());
    Assert.assertEquals(6,buffer.length());
    buffer.append(tmp,0,4);
    Assert.assertEquals(16,buffer.capacity());
    Assert.assertEquals(10,buffer.length());
    Assert.assertEquals("1212341234",buffer.toString());
  }
  