simulate_swipe.swift

  var simulateScrollingTimer: Timer?
  var scrollUp = false
  private func simulateScrolling() {
    collectionView.contentOffset = CGPoint.zero
    scrollUp = false
    simulateScrollingTimer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(simulateSwipe), userInfo: nil, repeats: true)
  }

  private func simulateSwipe() {
    guard collectionView.contentSize.height > 0
      else { return }
    var currentPosition = collectionView.contentOffset
    currentPosition.y += collectionView.bounds.height * (scrollUp ? -1.5 : 1.5)
    if currentPosition.y > collectionView.contentSize.height {
      scrollUp = true
      currentPosition.y = collectionView.contentSize.height - collectionView.bounds.height
    } else if currentPosition.y < 0 {
      currentPosition.y = 0
      if scrollUp {
        simulateScrollingTimer?.invalidate()
      }
    }
    collectionView.setContentOffset(currentPosition, animated: true)
  }

Scrolls all the way down and up again and then stops the timer.