Bandai Namco has announced that starting on Friday September 21st and going through Sunday September 23rd, there will be a network test for Dark Souls: Remastered. Each day the test will run from 5:00 pm to 9:00 pm Pacific time. You can download it from the eShop stating today. The network test takes place in the Undead Parish and gives access to both single player and multiplayer.
Dark Souls: Remastered is set to officially launch this upcoming October 19th 2018. And yes, a subscription to Nintendo Switch Online is required to be a part of the network test. Though Nintendo does offer a 7-day Switch Online trial in the eShop if you want to try it out for free. Your save data from the test will not carry over to the final game.
