c# - 如何将 NUnit 的 EqualTo().Within() 约束与自定义数据类型一起使用？

Question

我喜欢 NUnit 基于约束的 API。我经常使用这样的浮点比较:

double d = foo.SomeComputedProperty;

Assert.That(d, Is.EqualTo(42.0).Within(0.001));

很有可读性!

但是，如果我有一个自定义类，其相等性取决于浮点比较:

class Coord
{
  Coord(double radius, double radians)
  {
    this.Radius = radius;
    this.Radians = radians;
  }

  double Radius { get; }
  double Radians { get; }

  public override bool Equals(Object obj)
  {
    Coord c = obj as Coord;
    if (obj == null || c == null) return false;

    return c.Radians == this.Radians && c.Radius == this.Radius;
  }
}

我想像这样编写我的测试:

Coord reference = new Coord(1.0, 3.14);

// test another Coord for near-equality to a reference Coord:
Assert.That(testCoord, Is.EqualTo(reference).Within(0.001));

是否有可能像这样使用 NUnit？

Answer 1

以下是为 NUnit 3 编写的

使用 System.Numerics.Complex类作为一个简单的例子，我可以写一个测试

Assert.That(z1, Is.EqualTo(z2).Using<Complex>(NearlyEqual));

使用此比较功能:

internal static bool NearlyEqual(Complex z1, Complex z2)
{
    return Math.Abs(z1.Real - z2.Real) < 1e-10 &&
           Math.Abs(z1.Imaginary - z2.Imaginary) < 1e-10;
}

这为您提供了 juharr 评论中提到的比较器，并实现了您所要求的基础知识。它不允许我参数化容差，但它很接近。

为了完成要求，我想将测试编写为

Assert.That(z1, Is.EqualTo(z2).Within(new Complex(1e-10, 1e-10)));

但是，正如问题中所述，这并不容易。它需要一种新的约束扩展方法

public static class ComplexTestExtensions
{
    public static ComplexEqualConstraint WithinZ(this EqualConstraint constraint, Complex tolerance)
    {
        return new ComplexEqualConstraint(constraint) { Tolerance = tolerance };
    }
}

然后按照以下几行编写自定义约束:

public class ComplexEqualConstraint
    : EqualConstraint
{
    public ComplexEqualConstraint(EqualConstraint that)
        : base(that)
    {
    }

    public override ConstraintResult ApplyTo<TActual>(TActual actual)
    {
        bool success = false;
        if (actual is Complex z1)
        {
            Complex z2 = (Complex)this.Arguments[0];
            success = Math.Abs(z1.Real - z1.Real) < Tolerance.Real &&
                      Math.Abs(z1.Imaginary - z2.Imaginary) < Tolerance.Imaginary;
        }
        return new ConstraintResult(this, actual, success);
    }

    public new Complex Tolerance
    {
        get;
        set;
    } = Complex.Zero;
}