def test_empty_undo():
'''
Check that undoing an empty board doesn't break.
'''
patient = GameState(3)
patient.undo()
assert(patient.player_to_act() == BoardValues.X)
def test_winner_after_undo():
'''
Check that undoing a move after a win no longer results in a win.
'''
patient = GameState(3)
assert_no_winner(patient)
patient.play(patient._spaces.index(0, 0)) \
.play(patient._spaces.index(1, 0)) \
.play(patient._spaces.index(1, 1)) \
.play(patient._spaces.index(1, 2)) \
.play(patient._spaces.index(2, 2))
assert_X_wins(patient)
patient.undo()
assert_no_winner(patient)
assert(not patient.is_terminal())
assert(patient.num_legal_actions() == 5)