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]