Example from NSub list

NSubMisc.cs

using System.Collections.Generic;
using System.Linq;
using NSubstitute;
using NUnit.Framework;
using Shouldly;

namespace Workshop
{
    public class NSubMisc
    {
        public interface ICommand { }
        private class DerivedCommand : ICommand { }
        public interface IInterface { void SendCommand(ICommand c); }

        [Test]
        public void TestWhenDo()
        {
            var commands = new List<ICommand>();
            var sub = Substitute.For<IInterface>();
            sub.When(x => x.SendCommand(Arg.Any<ICommand>())).Do(c => commands.Add(c.Arg<ICommand>()));

            var c1 = new DerivedCommand();
            var c2 = Substitute.For<ICommand>();
            sub.SendCommand(c1);
            sub.SendCommand(c2);

            commands.Select(x => x).ShouldBe(new[] {c1, c2});
        }

    }
}