What makes a high quality, long-term test spinner?

1. Accuracy and reliability, obviously.

2. Usually a powerfully-spun (fizzing) stock delivery with lots of revolutions on it; but if not then plenty of bounce at slow-medium pace (e.g. Kumble, SF Barnes, Mendis).

3. A well-disguised variation. At the highest level is is vital that the variation be hard/ impossible to pick. If it is, then the variation need not be anything spectacular - a good 'arm ball' for a slow left arm orthodox/ of-spinner is as good as a doosra- or , and a legspinner's straight delivery is as good as a googly/ wrong-un.

Contrariwise, if the variation is easy to pick then it is pretty useless at the highest level; even if it is a spectacularly-turning googly, an excocet-missile flipper or a high-bouncing doosra.

Swann is evidence of all this. He is the best spinner in the world on the basis of accuracy and reliability, a high-rev off break and a straight 'gyro' ball. In particular he is better than any of the doosra bowlers, because his gyro variation is very difficult/ impossible to pick - unlike most doosras (exceptions being Murali, and perhaps Saeed Ajmal).