 cdata.deleteData('OK'.length, ' modified'.length);
  testing.expectEqual('OK', cdata.data)

  cdata.insertData('OK'.length-1, 'modified');
  testing.expectEqual('OmodifiedK', cdata.data);

  cdata.replaceData('OK'.length-1, 'modified'.length, 'replaced');
  testing.expectEqual('OreplacedK', cdata.data);

  testing.expectEqual('replaced', cdata.substringData('OK'.length-1, 'replaced'.length));
  testing.expectEqual('', cdata.substringData('OK'.length-1, 0));

  testing.expectEqual('replaced', cdata.substrin