public void DoesCalculateCorrectDifference() { var date1 = DateTime.Now; var date2 = date1.AddSeconds(_compareTime); var mockTime = new Mock <ITimeService>(); mockTime.Setup(x => x.GetCurrentTime()).Returns(date2); var elapseService = new ElapsedService(mockTime.Object); var difference = elapseService.GetElapsedTime(date1); ((int)difference.TotalSeconds).Should().Be(_compareTime); }