function getDiffLabel(diff) {
  switch (diff.type) {
    case 'error':
      return 'regression';
    case 'score':
      return getDeltaLabel(getDeltaStats(diff).delta, 'score');
    case 'numericValue':
    case 'itemCount':
    case 'itemDelta':
      return getDeltaLabel(getDeltaStats(diff).delta, 'audit');
    case 'itemAddition':
      return 'regression';
    case 'itemRemoval':
      return 'improvement';
    default:
      return 'neutral';
  }
}
@param {LHCI.AuditDiff} diff
@return {DiffLabel}