All you have to do to get one if head over to the Official Adidas Product Testing website and apply to become a product tester.
If selected they will send you free products from their vast range to try out and give some feedback on.
Please note: adidas does not pay money to its wear testers. You only get products.
All the information you need to apply to become an Adidas Product Tester can be found on the https://producttesting.adidas.com/en/requirements page.