写出一段测试代码 在准备类Fraction时，创建一个类nul1denominatoreexception，它必须是一个检查异常，如果类Fraction的对象的分母为0，则抛出其实例。将Fraction类的各种方法完整呈现出来

下面是一个例子，展示了如何在 Fraction 类中使用 NullDenominatorException：

class NullDenominatorException(Exception):
    pass


class Fraction:
    def __init__(self, numerator, denominator):
        if denominator == 0:
            raise NullDenominatorException("分母不能为0")
        self.numerator = numerator
        self.denominator = denominator

    def __str__(self):
        return f"{self.numerator}/{self.denominator}"

    def __add__(self, other):
        new_numerator = self.numerator * other.denominator + other.numerator * self.denominator
        new_denominator = self.denominator * other.denominator
        return Fraction(new_numerator, new_denominator)

    def __sub__(self, other):
        new_numerator = self.numerator * other.denominator - other.numerator * self.denominator
        new_denominator = self.denominator * other.denominator
        return Fraction(new_numerator, new_denominator)

    def __mul__(self, other):
        new_numerator = self.numerator * other.numerator
        new_denominator = self.denominator * other.denominator
        return Fraction(new_numerator, new_denominator)

    def __truediv__(self, other):
        new_numerator = self.numerator * other.denominator
        new_denominator = self.denominator * other.numerator
        return Fraction(new_numerator, new_denominator)

    def simplify(self):
        gcd = self._gcd(self.numerator, self.denominator)
        self.numerator //= gcd
        self.denominator //= gcd

    @staticmethod
    def _gcd(a, b):
        if b == 0:
            return a
        return Fraction._gcd(b, a % b)

下面是一段测试代码：

try:
    # 创建一个分母为0的分数
    f = Fraction(1, 0)
except NullDenominatorException as e:
    print("发生异常：", e)
else:
    print("分数为：", f)

# 创建两个分数
f1 = Fraction(1, 2)
f2 = Fraction(3, 4)

# 进行加法运算
f3 = f1 + f2
print(f"{f1} + {f2} = {f3}")

# 进行减法运算
f4 = f1 - f2
print(f"{f1} - {f2} = {f4}")

# 进行乘法运算
f5 = f1 * f2
print(f"{f1} * {f2} = {f5}")

# 进行除法运算
f6 = f1 / f2
print(f"{f1} / {f2} = {f6}")

# 简化分数
f7 = Fraction(2, 4)
print(f"原分数：{f7}")
f7.simplify()
print(f"简化后的分数：{f7}")

当分母为0时，运行上述代码会抛出 NullDenominatorException 异常。如果分母不为0，会进行加、减、乘、除、简化等运算，并输出结果。