How to mock object's indexer with private setter in NSubstitute?

Question

I have an interface that is defined like the following

 public interface IFoo
    {
        object this[string key] { get; }
    }

How can I mock this indexer using NSubstitute?

Answer 1

Call the indexer then use Returns:

var sub = Substitute.For<IFoo>();
sub["hello"].Returns("world");