Cron to observable Rx, retry and circuit breaker

cronToRxExample.cs

// via https://stackoverflow.com/questions/26597393/cron-observable-sequence

// and cloud patterns (circuit breaker, retry, etc) 
https://github.com/myquay/Solve.Reliability.Rx

// convert cron to time https://github.com/HangfireIO/Cronos
public static IObservable<int> Cron(string cron, IScheduler scheduler)
{
    var schedule = CrontabSchedule.Parse(cron);
    return Observable.Generate(0, d => true, d => d + 1, d => d,
        d => new DateTimeOffset(schedule.GetNextOccurrence(scheduler.Now.UtcDateTime)), scheduler);
}

[TestMethod]
public void TestCronInterval()
{
    var scheduler = new TestScheduler();
    var end = scheduler.Now.UtcDateTime.AddMinutes(10);
    const string cron = "*/5 * * * *";
    var i = 0;
    var seconds = 0;
    var sub = ObservableCron.Cron(cron, scheduler).Subscribe(x => i++);
    while (i < 2)
    {
        seconds++;
        scheduler.AdvanceBy(TimeSpan.TicksPerSecond);
    }
    Assert.IsTrue(seconds == 600);
    Assert.AreEqual(end, scheduler.Now.UtcDateTime);
    sub.Dispose();
}