Twitter is introducing e-commerce into its tweets. The “buy this product” button has been rumored for months, but Monday it was confirmed by the social media network. An initial test batch of mobile users will be able to purchase within a tweet itself, without ever leaving the application. Down the line, Twitter will expand it to desktop and more users. The “buy” button is being tested out in the Twitter wild with three initial partners – social shopping platform Fancy, art and digital content marketplace Gumroad and music merchandise site Musictoday. Twitter announced a range of individual sellers with the partnership, from Demi Lovato to Home Depot to Burberry.