char[] tmp = new char[] { '1', '2', '3', '4'};
buffer.append(tmp, 0, 2);
buffer.append(tmp, 0, 4);
buffer.append(tmp, 0, 0);
assertEquals(8, buffer.capacity());
assertEquals(6, buffer.length());
buffer.append(tmp, 0, 4);
assertEquals(16, buffer.capacity());