def test_incorrect_R_relations(dummy):
impossible_father_in_law = Person(sex="female")
assert not impossible_father_in_law.can_be_father_in_law_of(dummy)
father_in_law = Person(sex="male")
impossible_son_in_law = Person(sex="female")
assert not father_in_law.can_be_father_in_law_of(impossible_son_in_law)
assert not father_in_law.can_be_father_in_law_of(father_in_law)
def test_correct_R_relations():
father_in_law = Person(sex="male")
son_in_law = Person(sex="male")
assert father_in_law.can_be_father_in_law_of(son_in_law)