Nunit Assertion for an empty intersection between collection - vb.net

Question

I've looked all around, and can't quite figure this one out, and my multitude of trial and error attempts have all been useless.
I have a list of user names (we'll call 'original list') one object is returning
I have a list of user names (we'll call 'filtration list') another object is returning
I am testing a method that returns all of the items from the original list not in the filtration list.
Ideally what I want is something like
Assert.That(returnedList, Has.No.Members.In(filtrationList))
So far the only thing I can do is iterate over the filtrationList and do
Assert.That(returnedList, Has.None.EqualTo(filteredUser))

Answer 1

With nunit you can create any custom constraint.
If you want to verify two collections for intersection, you can create something like this:
public class Intersects : CollectionConstraint
{
private IEnumerable _collection2;
public Intersects(IEnumerable collection2)
: base(collection2)
{
_collection2 = collection2;
}
public static Intersects With(IEnumerable arg)
{
return new Intersects(arg);
}
protected override bool doMatch(IEnumerable collection)
{
foreach (object value in collection)
{
foreach (object value2 in _collection2)
if (value.Equals(value2))
return true;
}
return false;
}
public override void WriteDescriptionTo(MessageWriter writer)
{
//You can put here something more meaningful like items which should not be in verified collection.
writer.Write("intersecting collections");
}
}
usage is pretty simple:
string[] returnedList = new string[] { "Martin", "Kent", "Jack"};
List<string> filteredUsers = new List<string>();
filteredUsers.Add("Jack");
filteredUsers.Add("Bob");
Assert.That(returnedList, Intersects.With(filteredUsers));