def test_duplicate_max(): numbers = [2, 4, 3, 1, 4] assert get_duplicate(numbers) == 4
def test_duplicate_none_input(): numbers = [] assert get_duplicate(numbers) == None
def test_duplicate_invalid_input(): numbers = 1 assert get_duplicate(numbers) == None
def test_duplicate_input_cross_lower(): numbers = [-1, 1, 2, 3] assert get_duplicate(numbers) == None
def test_duplicate_no(): numbers = [1, 2, 3, 0] assert get_duplicate(numbers) == None
def test_duplicate_input_cross_lower_same(): numbers = [-1, -1] assert get_duplicate(numbers) == None
def test_duplicate_input_cross_upper(): numbers = [1, 2, 3, 4] assert get_duplicate(numbers) == None
def test_duplicate_min(): numbers = [2, 1, 3, 1, 4] assert get_duplicate(numbers) == 1
def test_duplicate_input_cross_upper_same(): numbers = [3, 3] assert get_duplicate(numbers) == None
def test_duplicate_same(): numbers = [1, 1] assert get_duplicate(numbers) == 1
def test_duplicate_order(): numbers = [0, 1, 1, 2] assert get_duplicate(numbers) == 1
def test_duplicate_multi(): numbers = [2, 4, 2, 1, 4] assert get_duplicate(numbers) in [2, 4]