def multiply(a, b):
    """返回两个数字的乘积"""
    return a * b


def divide(a, b):
    """返回两个数字的商，b不能为零"""
    if b == 0:
        raise ValueError("除数不能为零")
    return a / b


if __name__ == "__main__":
    # 测试乘法
    assert multiply(3, 4) == 12
    assert multiply(-2, 5) == -10
    assert multiply(0, 100) == 0
    print("乘法测试通过")

    # 测试除法
    assert divide(10, 2) == 5
    assert divide(9, 3) == 3
    assert divide(5, 2) == 2.5
    print("除法测试通过")

    # 测试除零异常
    try:
        divide(1, 0)
        print("ERROR: 除零异常未触发")
    except ValueError as e:
        assert str(e) == "除数不能为零"
        print("除零异常测试通过")

    print("所有测试通过")