单元测试失败 AreEquals() 和 ToString()

Question

我的主要方法是：

using System;
namespace Rational
{
   public class Rational
   {
       public int Denom { get; private set; }
       public int Numer { get; private set; }
       public Rational(int numerator = 0, int denominator = 1)
       {
           Denom = denominator;
           Numer = numerator;
       }
       public void IncreaseBy(Rational num)
       {
           Numer = Numer * num.Denom + num.Denom * Denom;
           Denom = Denom * num.Denom;
       }
       public void DecreaseBy(Rational num)
       {
           Numer = Numer * num.Denom - num.Denom * Denom;
           Denom = Denom * num.Denom;
       }
       override public String ToString() { return (Numer + "/" + Denom); }
   }

我调用我的方法的程序是：

using System;
namespace Rationals
{
   public class Rationals

   {

       class Program
       {
           static void Main(string[] args)
           {
               Rational num1 = new Rational(10, 8);
               Rational num2 = new Rational(8, 10);
               Console.WriteLine("1st number is:   " + num1);
               Console.WriteLine("2nd number is:   " + num2);
               num1.IncreaseBy(num2);
               Console.WriteLine("1st number + 2nd number = " + num1);
               num1.DecreaseBy(num2);
               Console.WriteLine("1st number - 2nd number = " + num2);
           }
       }
   }
}

我必须编写一个单元测试来测试我的IncreaseBy() 以及我的DecreaseBy() 以及最后的ToString()。 有人可以帮帮我吗？！！？

这是我迄今为止在 UnitTest 中所拥有的，请尽可能多地使用它。 我无法使测试通过它不断出现不同的答案，而且 ToString() 会引发错误。

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Rationals_123456789;

namespace ratonalstest
{
   [TestClass]
   public class UnitTest1
   {
       [TestMethod]
       public void DecreaseByTest()
       {
           int num = 1, den = 6, num1 = 2, den1 = 9;
           Rational fraction1 = new Rational(num, den);
           Rational fraction2 = new Rational(num1, den1);
           Rational expectedFraction = new Rational(-1, 18);

           //when
           fraction1.DecreaseBy(fraction2);

           //then
           Assert.AreEqual(fraction1.Numer, expectedFraction.Numer);
           Assert.AreEqual(fraction1.Denom, expectedFraction.Denom);

       }
       [TestMethod]
       public void IncreaseByTest()
       {
           int num = 1, den = 4, num1 = 1, den1 = 4;
           Rational fraction1 = new Rational(num, den);
           Rational fraction2 = new Rational(num1, den1);

           Rational expectedFraction = new Rational(7, 18);

           //when
           fraction1.IncreaseBy(fraction2);

           //then
           Assert.AreEqual(fraction1.Numer, expectedFraction.Numer);
           Assert.AreEqual(fraction1.Denom, expectedFraction.Denom);

           //when
           fraction1.DecreaseBy(fraction2);

           //then
           Assert.AreEqual(fraction1.Numer, expectedFraction.Numer);
           Assert.AreEqual(fraction1.Denom, expectedFraction.Denom);

       }

       [TestMethod]
       public void ToString()
       {
           int num = 1, den = 6, num1 = 2, den2 = 9;
           Rational fraction1 = new Rational(num, den);
           Rational fraction2 = new Rational(num1, den2);

           string expectedString = "1/6";
           string outputString = fraction1.ToString();

          //then
           Assert.AreEqual(expectedString, outputString);

       }
   }
}

Answer 1

您的代码有两个问题。

1. 你计算结果错误
2. 你没有标准化分数

第一个问题是这两个表达式：

Numer = Numer * num.Denom + num.Denom * Denom;
Numer = Numer * num.Denom - num.Denom * Denom;

应该使用num.Numer而不是num.Denom所以这些是正确的：

Numer = Numer * num.Denom + num.Numer * Denom;
Numer = Numer * num.Denom - num.Numer * Denom;

现在，这仍然不会使您的测试通过，但现在让我们尝试您的代码：

Rational fraction1 = new Rational(1, 6);
Rational fraction2 = new Rational(2, 9);

fraction1.DecreaseBy(fraction2);
Console.WriteLine(fraction1.ToString());

这输出：

-3/54

您的测试需要-1/18 ，但这些实际上是相同的数字。 您的测试必须通过引入分数归一化或以不同的方式进行比较来处理这种差异。

---

最后我有一些tips：

1. 使 Rational 类型成为只读的不可变struct
2. 实现不改变现有值而是计算结果并将结果作为新的 Rational 值返回的适当运算符
3. 添加对归一化的支持，这通常通过将分子和分母除以 GCD 值来完成，并确保最多只有分子是负数（没有负分母）