An example of simple messaging with observables

PubSub.cs

/*
One: Hi
Two: Hi
One: Hi
Two: Hi
One: Hi
Two: Hi
One: Hi
Two: Hi
One: Hi
Two: Hi
One: Hi
Two: Hi
*/

using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Reactive.Disposables;
using System.Threading.Tasks;

namespace UnitTestProject1
{
    public class Subscriber : IObserver<string>
    {
        Action<string> _action;

        public Subscriber(Action<string> action) => _action = action;

        public void OnCompleted() { }

        public void OnError(Exception error) { }

        public void OnNext(string value) => _action(value);
    }

    public class Publisher : IObservable<string>
    {
        List<IObserver<string>> _observers = new List<IObserver<string>>();

        public Publisher()
        {
            Task.Run(async () =>
            {
                //Loop forever
                while (true)
                {
                    //Get some data, publish it with OnNext and wait 500 milliseconds
                    _observers.ForEach(o => o.OnNext(GetSomeData()));
                    await Task.Delay(500);
                }
            });
        }

        private string GetSomeData() => "Hi";

        public IDisposable Subscribe(IObserver<string> observer)
        {
            _observers.Add(observer);
            return Disposable.Create(() => { });
        }
    }

    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public async Task Messaging()
        {
            var subscriber1 = new Subscriber((message) => Debug.WriteLine($"One: {message}"));
            var subscriber2 = new Subscriber((message) => Debug.WriteLine($"Two: {message}"));
            var publisher = new Publisher();
            publisher.Subscribe(subscriber1);
            publisher.Subscribe(subscriber2);
            await Task.Delay(3000);
        }
    }
}