public void ShouldUpdate() { Flight flight = new Flight { id = 1, Reg = "X" }; var flights = new ObservableCollection <Flight>(); flights.Add(flight); flights.Add(new Flight { id = 2 }); flights.Add(new Flight { id = 3 }); FlightData.Update(new Flight { id = 1, Reg = "Y" }, flights); var updated = flights.Where(x => x.id == 1).First(); Assert.AreEqual("Y", updated.Reg); }