Determined not to repeat a holiday season that left millions of packages delivered too late and customers seething, United Parcel Service Inc (UPS.N) and FedEx Corp (FDX.N) are investing heavily in new infrastructure – but the continued dynamic growth of e-commerce will test those efforts. The world’s two largest shipping companies are building new facilities, adding more temporary holiday workers and pushing retailers to help them avoid a recurrence of a pre-Christmas shipping logjam.