#determine_best_move: when opponent has 2 in row, it blocks him
#determine_best_move: when it has 2 non-blocked lines of 2, it forks
#determine_best_move: when opponent can fork, it forces him into defending
#determine_move: Defensive attack does not result in opponent opportunity to fork
#determine_best_move: computer blocks the opponent's fork
Reword test header