How to deal with private member accessor and collections?

I have a class hierachy like this

public class A
{
    protected开发者_JAVA百科 class B 
    {
        String Name { get; set; }
    }

    protected class C : KeyedCollection<String, B> 
    {
        // ...
    }

    protected C Collection { get; }

    // ...

    public A Copy () 
    {
        // Creates a deep copy of this instance.
    }
}

Now I'd like to write a unit test to compare if two instances of A have the same items B inside the property KeyedCollection. However, I'm not being able to perform a foreach loop into the A instances. What I had tried,

[TestClass]
public class TestClass
{
    public void ATest()
    {
        A original = new A();
        A copy = A.Copy();

        // ...

        A_Accessor originalAccessor = A_Accessor.AttachShadow(original);
        A_Accessor copyAccessor = A_Accessor.AttachShadow(copy);

        foreach(var originalItem in originalAccessor.Collection)
        {
            var copyItem = copyAccessor[originalItem.Name];
            Assert.AreEqual(originalItem, copyItem);
        }
    }
}

This code doesn't even compile because the C class accessor doesn't implements the IEnumerable interface (it doesn't implement any interface from KeyedCollection class). Does anyone have an idea about how can I overcome this issue?

The error message I'm getting is

foreach statement cannot operate on variables of type 'C' because 'A_Accessor.C' does not contain a public definition for 'GetEnumerator'

I just tried to compile your example: As expected I got an Error

Inconsistent accessibility: field type 'A.C' is less accessible than field 'A.Collection'.

Basically that means that you cannot declare a protected property using a private type. So it's not a problem with your test code but with the code to be tested ...

EDIT

You could use originalAccessor.Collection.Target and cast it to ICollection. Of course you can only enumerate over objects in this case, so you'll have to cast each item again:

foreach (var item in (originalAccessor.Collection.Target as ICollection)) {
   A_Accessor.B casted = A_Accessor.B.AttachShadow(item);
   var copyItem = copyAccessor[casted.Name];
   Assert.AreEqual(casted, copyItem);
}

It's not clear how you're managing to expose a private class type via a protected property to start with, but as C derives from KeyedCollection it should already inherit the implementation of IEnumerable<B>.

It's not really clear what you're trying to do, but you should still be able to iterate over the collection... if you can even see the property. I suspect your code doesn't compile for other reasons - because C is declared in terms of a private member type, despite being protected, and because you're trying to access C from a different class in the first place (despite it being protected).

Actually, the solution I found was very similiar to Martin's suggestion:

var originalItems = 
    from item in (originalAccessor.Collection.Target as IEnumerable).Cast<Object>()
    select A_Accessor.B.AttachShadow(item);

var copyItems = 
    from item in (copyAccessor.Collection.Target as IEnumerable).Cast<Object>()
    select A_Accessor.B.AttachShadow(item); 

foreach(var original in originalItems) 
{ 
    String originalName = original.Name;
    A_Accessor.B copy = copyItems.First(b => b.Name == originalName);

    // ...
}

Thanks for all your assitance! Carlos.

It seems to me that you are testing an implementation detail, not the intended API level for users of your library.