The XP Programmer's Cube is an artifact that captures the key activities in a day in the life of an XP programmer. A state machine is a traditional way to show a set of activities and the possible transitions between them. Many teams use it to get focused for the day. The fixed starting time helps remind the team to work a 40-hour week.
All production code is produced by a pair.
The typist thinks tactically, the partner thinks strategically. Switch roles periodically. Test Write only small bits of unit test code at a time. Verify that the test fails before coding. Test everything that could possibly break.