Target and Walmart are separately testing home package deliveries a la Amazon.com at a time when traditional carriers like FedEx, United Parcel Service and the U.S. Postal Service are straining under demand caused by the continuing growth in online sales. Target has been using third-party drivers working with its Shipt service to make deliveries in its home city of Minneapolis. Walmart has been using electric vans since January to make deliveries in areas near the company’s headquarters.