using System;

using System.Collections.Generic;

using NSubstitute;

public class Program

{

    public static void Main()

    {

        var entityIds = new[] { 0UL, 1UL };

        var entities = new List<IManipulableObject>();

        var mockManipulableObjectLookup_ = Substitute.For<IManipulableObjectLookup>();

        var nodesMocks = new List<string> { "Hello", "World" };

        mockManipulableObjectLookup_!

                .When(x =>

                  x.GetManipulableObjects(Arg.Any<IEnumerable<ulong>>(), ref entities))

                .Do(x => {

                    Console.WriteLine(x[1]);

                  var refObjects = x[1] as List<IManipulableObject>;

                  foreach (var node in nodesMocks) {

                    var manipulableObject = Substitute.For<IManipulableObject>();

                    manipulableObject!.SgNode.Returns(node);

                    refObjects!.Add(manipulableObject);

                  }

                });

        mockManipulableObjectLookup_.GetManipulableObjects(entityIds, ref entities);

        entities.Dump();

    }

}

​

public interface IManipulableObjectLookup 

{

    void GetManipulableObjects(IEnumerable<ulong> ids, ref List<IManipulableObject> a);

}

public interface IManipulableObject

{

    string SgNode { get; }

}