1: public class Vector

   2: {

   3:     private static void EnsureNotNull(object value, string parameterName)

   4:     {

   5:         if (null == value)

   6:         {

   7:             throw new ArgumentNullException(parameterName);

   8:         }

   9:     }

  10:     public double X { get; internal set; }

  11:     public double Y { get; internal set; }

  12:  

  13:     public Vector(double x, double y)

  14:     {

  15:         this.X = x;

  16:         this.Y = y;

  17:     }

  18:  

  19:     public override bool Equals(object obj)

  20:     {

  21:         Vector vector = obj as Vector;

  22:         if (null == vector)

  23:         {

  24:             return false;

  25:         }

  26:  

  27:         return this.X == vector.X && this.Y == vector.Y;

  28:     }

  29:  

  30:     public static Vector operator + (Vector v1, Vector v2)

  31:     {

  32:         EnsureNotNull(v1, "v1");

  33:         EnsureNotNull(v2, "v2");

  34:         return new Vector(v1.X + v2.X, v1.Y+ v2.Y);

  35:     }

  36:  

  37:     public override int GetHashCode()

  38:     {

  39:         return this.X.GetHashCode() ^ this.Y.GetHashCode();

  40:     }

  41: }

在单元测试项目Test中，定义如下一个VectorFixture类型，用于测试向量相加的逻辑。为了测试方便，我在这里希望直接设置Vector的X和Y属性，而这两个属性的Set方式是Internal的。