This is an implementation of KataTennis
| description | balls won | score |
|---|---|---|
| before game starts | 0 - 0 | |
| single ball | s | 15 - 0 |
| same player wins 2 balls | rr | 30 - 0 |
| same player wins 3 balls | sss | 40 - 0 |
| same player wins 4 balls - game ends | rrrr | r winner |
| both players win balls | srss | 40 - 15 |
| deuce 8 balls | srsrsrsr | deuce |
| deuce 10 balls | srsrsrsrsr | deuce |
| advantage | srsrsrsrr | r advantage |
| game ends after advantage | srsrsrsrss | s winner |
| deuce after advantage | srsrsrsrsa | deuce |
s = server r = receiver