C# Date类GetMonthOffset方法测试失败，求技术方向指引

我在做学校作业，卡壳好几天了，不是要找代做，只想要解决思路。给定Date(1, 1, 2014)，需要实现函数返回该月份的offset。我不知道怎么把Date构造函数和之前测试用的枚举关联起来，也不确定要不要这么做。前面几个单元测试都过了，但最后一个GetMonthOffsetForSpecifiedDate失败了：针对janDate的断言显示预期是Date.Offset.October，实际得到Date.Offset.May，我搞不懂哪里出问题。

已通过的单元测试代码 #

// 查找星期几的名称
[TestMethod]
public void GetDayNameFromEnum()
{
    Assert.AreEqual("Sunday", Date.DayOfWeek.Sunday.ToString());
    Assert.AreEqual("Monday", Date.DayOfWeek.Monday.ToString());
    Assert.AreEqual("Tuesday", Date.DayOfWeek.Tuesday.ToString());
    Assert.AreEqual("Wednesday", Date.DayOfWeek.Wednesday.ToString());
    Assert.AreEqual("Thursday", Date.DayOfWeek.Thursday.ToString());
    Assert.AreEqual("Friday", Date.DayOfWeek.Friday.ToString());
    Assert.AreEqual("Saturday", Date.DayOfWeek.Saturday.ToString());
}

// 从枚举获取月份名称
[TestMethod]
public void MonthNameFromEnum()
{
    Assert.AreEqual("January", Date.MonthName.January.ToString());
    Assert.AreEqual("February", Date.MonthName.February.ToString());
    Assert.AreEqual("March", Date.MonthName.March.ToString());
    Assert.AreEqual("April", Date.MonthName.April.ToString());
    Assert.AreEqual("May", Date.MonthName.May.ToString());
    Assert.AreEqual("June", Date.MonthName.June.ToString());
    Assert.AreEqual("July", Date.MonthName.July.ToString());
    Assert.AreEqual("August", Date.MonthName.August.ToString());
    Assert.AreEqual("September", Date.MonthName.September.ToString());
    Assert.AreEqual("October", Date.MonthName.October.ToString());
    Assert.AreEqual("November", Date.MonthName.November.ToString());
    Assert.AreEqual("December", Date.MonthName.December.ToString());
}

// 查找每个月份的起始日偏移值
[TestMethod]
public void TestMonthOffsetEnums()
{
    Assert.AreEqual(0, (int)Date.Offset.January);
    Assert.AreEqual(3, (int)Date.Offset.February);
    Assert.AreEqual(3, (int)Date.Offset.March);
    Assert.AreEqual(6, (int)Date.Offset.April);
    Assert.AreEqual(1, (int)Date.Offset.May);
    Assert.AreEqual(4, (int)Date.Offset.June);
    Assert.AreEqual(6, (int)Date.Offset.July);
    Assert.AreEqual(2, (int)Date.Offset.August);
    Assert.AreEqual(5, (int)Date.Offset.September);
    Assert.AreEqual(0, (int)Date.Offset.October);
    Assert.AreEqual(3, (int)Date.Offset.November);
    Assert.AreEqual(5, (int)Date.Offset.December);
}

// 查找给定日期的月份偏移值
[TestMethod]
public void GetMonthOffsetForSpecifiedDate()
{
    Date janDate = new Date(1, 1, 2014);
    Assert.AreEqual(Date.Offset.January, janDate.GetMonthOffset());

    Date junDate = new Date(6, 16, 2014);
    Assert.AreEqual(Date.Offset.June, junDate.GetMonthOffset());

    Date decDate = new Date(12, 12, 2014);
    Assert.AreEqual(Date.Offset.December, decDate.GetMonthOffset());
}

当前Date类代码 #

public class Date
{
    public int Day {  get; set; }
    public int Month { get; set; }  
    public int Year { get; set; }

    public Date(int month, int day, int year) 
    {   
        Day = day;
        Month = month;
        Year = year;
    }

    public enum DayOfWeek { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }

    public enum MonthName { January = 1, February, March, April, May, June, July, August, September, October, November, December }

    public enum Offset { January = 0, February = 3, March = 3, April = 6, May = 1, June = 4, July = 6, August = 2, September = 5, October = 0, November = 3, December = 5 }

    public Offset GetMonthOffset()
    {
        return (Offset) Month;
    }
}

问题根源与解决思路 #

1. 核心错误：当前GetMonthOffset()方法直接将Month字段（比如1代表一月）强转为Offset枚举，但Offset枚举的成员值和月份数字完全不对应。例如Month=1强转时，会匹配枚举中值为1的成员，也就是Offset.May，这就是测试失败的直接原因。
2. 正确逻辑：需要建立月份数字（1-12）到对应Offset枚举成员的映射，而不是直接强转数值。比如：
   • 月份1 → Offset.January
   • 月份2 → Offset.February
   • ...以此类推到月份12 → Offset.December
3. 实现方案参考：
   • 字典映射：在Date类中定义一个静态字典，提前存储月份与Offset的对应关系：

     private static readonly Dictionary<int, Offset> _monthToOffsetMap = new Dictionary<int, Offset>
     {
         {1, Offset.January},
         {2, Offset.February},
         {3, Offset.March},
         {4, Offset.April},
         {5, Offset.May},
         {6, Offset.June},
         {7, Offset.July},
         {8, Offset.August},
         {9, Offset.September},
         {10, Offset.October},
         {11, Offset.November},
         {12, Offset.December}
     };
     

     然后在GetMonthOffset()中返回_monthToOffsetMap[Month]。
   • Switch-Case：直接在GetMonthOffset()方法中用switch语句匹配月份：

     public Offset GetMonthOffset()
     {
         return Month switch
         {
             1 => Offset.January,
             2 => Offset.February,
             3 => Offset.March,
             4 => Offset.April,
             5 => Offset.May,
             6 => Offset.June,
             7 => Offset.July,
             8 => Offset.August,
             9 => Offset.September,
             10 => Offset.October,
             11 => Offset.November,
             12 => Offset.December,
             _ => throw new ArgumentOutOfRangeException(nameof(Month))
         };
     }
     

内容的提问来源于stack exchange，提问作者Bigcheese