如何使用私有方法对集合进行单元测试，检查是否已到达集合末尾

Question

我知道这可能是基本的东西，但如果我有一个在构造函数中初始化的私有字段集合，例如

public blah()
{
  _brushes = new List<Brush> { Brushes.Red, Brushes.Blue, Brushes.Green };
}

然后我有一个方法可以设置它（但也可以做很多其他事情）例如

public CreateModel(){
// does stuff
_model.Brush = GetNextBrush();
// does stuff
}

然后是私有方法，例如

private Brush GetNextBrush()
{
  var brush = _brushes[_index];
  _index++;

  if (_index == _brushes.Count)
  {
    _index = 0;
  }
  
  return brush;
}

对其进行单元测试的适当方法是什么？将画笔提取到具有接口的服务中并将其传递到构造函数中？看起来有点矫枉过正，但我可能错过了一些东西。我不想公开该方法 - 似乎是错误的。

非常感谢

-杰妮

更大的摘录：

public class vm : IViewModel
{
  private readonly List<Brush> _brushes;
  private int _brushIndex;
  private readonly _modelCollection;

  public vm(IModelCollection modelCollection)
  {
    _modelCollection = modelCollection;
    _brushes = new List<Brush> { Brushes.Red, Brushes.Blue, Brushes.Green };
  }

  public void AddSig(ISigModel sigModel)
  {    
    _model.Brush = GetNextBrush();
    if (sigModel.IsAtt)
    {
      sigModel.Process = "StartEvent";
    }
    _modelCollection.AddSig(sigModel);
    StartCSUpdatingEvent();
  }

    private Brush GetNextBrush()
    {
      var brush = _brushes[_index];
      _index++;
    
      if (_index == _brushes.Count)
      {
        _index = 0;
      }
      
      return brush;
    }
}

Answer 1

解决方案是将

GetNextBrush()

移至一个单独的类中，该类只有一个职责：生成下一个画笔。

public class BrushGenerator
{
   private List<Brush> _brushes = new List<Brush> { Brushes.Red, Brushes.Blue, Brushes.Green };

   private int _index = 0;

   public Brush GetNextBrush()
   {
     var brush = _brushes[_index];
     _index++;

     if (_index == _brushes.Count)
     {
        _index = 0;
     }
  
    return brush;
  }
}

在包含

CreateModel()

的类中，您可以创建此类的实例：

private BrushGenerator _brushGenerator = new BrushGenerator();
public CreateModel(){
// does stuff
_model.Brush = _brushGenerator .GetNextBrush();
// does stuff
}

现在您可以为您的

BrushGenerator

类编写单元测试：

[DataRow(1, Brushes.Red)]
[DataRow(2, Brushes.Blue)]
[DataRow(3, Brushes.Green)]
[DataRow(4, Brushes.Red)]
[DataTestMethod]
public void CorrectBrushIsReturned(int times, Brushes expectedBrush)
{
   var brushGenerator = new BrushGenerator();
   Brushes result = Brushes.None;

   for(int i = 0; i < times; i++)
   {
      result = brushGenerator.GetNextBrush();
   }

   Assert.AreEqual(expectedBrush, result);
}