def test_2():
assert select_max([0]) == 0
def test_1():
assert select_max([1, 2, 3]) == 3
def test_6():
assert select_max([]) == None
def test_5():
assert select_max([-10, -2, 1]) == 1
def test_4():
assert select_max([-10, -2, -8]) == -2
def test_3():
assert select_max([0, 0, 0]) == 0