TDD demo: spec

A program to score a game of ten-pin Bowling.

Write a class named "Game" that has two methods:
 - roll(pins) is called each time the player rolls a ball.  The argument is the number of
   pins knocked down.
 - score() is called only at the very end of the game.  It returns the total score for
   that game.

Rules of ten-pin bowling:
1. The game consists of 10 frames.  In each frame the player has two opportunities to
   knock down 10 pins.  The score for the frame is the total number of pins knocked down,
   plus bonuses for strikes and spares.
2. A spare is when the player knocks down all 10 pins in two tries.  The bonus for that
   frame is the number of pins knocked down by the next roll.  So in frame 3 above, the
   score is 10 (the total number knocked down) plus a bonus of 5 (the number of pins
   knocked down on the next roll.)
3. A strike is when the player knocks down all 10 pins on his first try.  The bonus for
   that frame is the value of the next two balls rolled.
4. In the tenth frame a player who rolls a spare or strike is allowed to roll the extra
   balls to complete the frame.  However no more than three balls can be rolled in tenth
   frame.

Steps in Test-Driven Development:

1. WRITE A FAILING TEST.
   Write the shortest possible failing test that exercises the desired behaviour.
   Observe it failing in the expected way.

2. MAKE IT PASS.
   Optimise for development speed.  All tests should pass.

3. REFACTOR
   Optionally, refactor the code, ensuring that the tests continue to pass.