title: Unit test IObservable<T> with ObserveOnDispatcher
body: <p>I need to test piece of code </p>
  
  <pre><code>        var watcher = new FakeIFileSystemWatcher();
          watcher.FilesToBeImported
              .ObserveOnDispatcher()
              .Subscribe(list.Add);
  </code></pre>
  
  <p>so I created this little unit test but I can't make it pass cause list.Count is always 0</p>
  
  <pre><code>    [Test]
      public void Foo()
      {
          var list = new List&lt;string&gt;();
  
          var watcher = new FakeIFileSystemWatcher();
          watcher.FilesToBeImported
              .ObserveOnDispatcher()
              .Subscribe(list.Add);
  
          Task task = Task.Factory.StartNew(() =&gt;
          {                
              watcher.AddFile("cc");
              watcher.AddFile("cc");
              watcher.AddFile("cc");
          }, TaskCreationOptions.LongRunning);
          Task.WaitAll(task);
  
          Assert.AreEqual(3, list.Count);
      }
  </code></pre>
  
  <p>if I comment out the method </p>
  
  <pre><code>            .ObserveOnDispatcher()
  </code></pre>
  
  <p>it pass but how can I get it working also with ObserveOnDispatcher() ?</p>