public void should_return_authors() { ICollection <Speaker> _speakers = new List <Speaker>(); Exception _ex = new Exception(); ManualResetEvent done = new ManualResetEvent(false); IGatewayService sut = new GatewayService(); sut.GetAuthors((authors, ex) => { _speakers = authors; _ex = ex; done.Set(); }); done.WaitOne(); Assert.IsNull(_ex); Assert.IsTrue(_speakers.Count > 0); }