/// <summary>
/// Called when this TestSubscriber gets subscribed to a source
/// with the ISubscription representing the connection between the two.
/// </summary>
/// <param name="subscription">The ISubscription from the upstream.</param>
public void OnSubscribe(ISubscription subscription)
{
hasSubscribed = true;
SubscriptionHelper.DeferredSetOnce(ref upstream, ref requested, subscription);
}
