At 'I Code Java' Pavel Dabrytski and Rory Preddy did a great presentation on ping-pong TDD.
I paired (It was more like rally than ping-pong.) with the brilliant Steven Ndaye and knocked up the formatter in about 10-15 minutes and later on added the parser in about 5 minutes.
The following day Frank Smith showed us how to use Spock to do the testing.
Kotlin conversion!!