使用jest断言时，匹配器函数应返回以下格式的对象

{
  pass: Boolean, // 表示断言是否通过
  message: () => String, // 返回一个函数，该函数返回断言失败时的错误信息
}

function isEven(num) {
  return {
    pass: num % 2 === 0,
    message: () => `${num} is not an even number`,
  };
}

test('should return true for even numbers', () => {
  expect(isEven(2)).toBe(true);
  expect(isEven(4)).toBe(true);
});

test('should return false for odd numbers', () => {
  expect(isEven(3)).toBe(false);
  expect(isEven(5)).toBe(false);
});