遵循 C# 中的给定单元测试时，如何正确删除从 void functionRemove 中的列表 ILine 继承接口的对象？

Question

I have interface ILine that is inherited by the class Line . ILine is defined like this:

interface ILine {

    string Name { get; }
    ICity City { get; }
    IEnumerable<IStation> Stations { get; }
    IEnumerable<ITrain> Trains { get; }

    IStation Previous(IStation s);
    IStation Next(IStation s);
    void AddBefore(IStation toAdd, IStation before = null);
    void Remove(IStation s);

}

In the current context I am working with in the method void Remove (IStation s) and I am trying to pass following unit test that tests stations can be removed and then re-added.

The Unit Test:

public void stations_can_be_removed()
{
    ICity c = CityFactory.CreateCity("Paris");
    ILine l = c.AddLine("RER B");
    IStation s = c.AddStation("Opera", 0, 0);
    Action action = (() => l.Remove(s));
    action.ShouldThrow<ArgumentException>();
    l.AddBefore(s);
    action = (() => l.Remove(s));
    action.ShouldNotThrow();
    l.Stations.Count().Should().Be(0);
    s.Lines.Count().Should().Be(0);
}

public void stations_can_be_removed_then_re_added()
{
    ICity c = CityFactory.CreateCity("Paris");
    ILine l = c.AddLine("RER B");
    IStation s = c.AddStation("Opera", 0, 0);

    l.AddBefore(s);
    s.Lines.Count().Should().Be(1);
    l.Remove(s);
    s.Lines.Count().Should().Be(0);

    Action action = (() => l.AddBefore(s));
    action.ShouldNotThrow();
    l.Stations.Count().Should().Be(1);
    s.Lines.Count().Should().Be(1);
}

I have tried to do the following code to pass the test mainly in the function void Remove . However, the unit test breaks at the line 7 where I throw exception. I guess my approach is wrong how to test this unit test mainly how I defined my exception by:

if (((List<ILine>)s.Lines).Remove(s))
{
    throw new ArgumentException();
}

public IEnumerable<IStation> Stations
{
    get{ return _stations; }
}

public IStation Next(IStation s)
{
    if (!_stations.Contains(s)) 
      throw new ArgumentException();
    var index = _stations.IndexOf(s);
    var isLast = index == _stations.Count -1;
    if (isLast) { return null;}
    return _stations[index + 1];
}

public IStation Previous(IStation s)
{
    if (!_stations.Contains(s))
        throw new ArgumentException();
    var index = _stations.IndexOf(s);
    var isFirst = index == 0;
    if (isFirst) { return null;}
    return _stations[index - 1];
}

public void AddBefore(IStation toAdd, IStation before = null)
{
    if (toAdd == null || _stations.Contains(toAdd)) 
        throw new ArgumentException();
    ((List<Line>)toAdd.Lines).Add(this);

    var index = (before != null) ? _stations.IndexOf(before) : -1;
    if (index > -1)
        _stations.Insert(index, toAdd);
    else
        _stations.Add(toAdd);
}

public void Remove(IStation s)
{
    _stations.Remove(s);
    if (((List<ILine>)s.Lines).Remove(s))
        throw new ArgumentException();

}

Answer 1

List<T>.Remove() returns true when it succeeds, therefore it throws the exception as your code instructs.

You probably want to throw said exception if it doesn't succeed:

if (!((List<ILine>)s.Lines).Remove(s))

But this is about the tenth question about this design, five of which you or others have deleted, and as I've suggested under multiple previous invocations, you may want to scratch this design and start over. A List<ILine> cannot contain an IStation , unless IStation inherits ILine , which is not logical (inheritance implies an is-a relation, and a station isn't a line).