We have a general testset, including models from Apple, Xiaomi, Oppo, Google, OnePlus, Samsung, Huawei, LG, Sony, HTC, Nokia, and more. For every release we run specific tests on all test devices. The test devices have been selected based on screen size, popularity, known previous issues and performance.
For Android devices, we test from Android version 5.0 and onwards and have models that run every major version of Android. For Apple devices, we test on older and newer iPhones, iPod Touches and iPads.
The majority of our testing is performed on devices that are relatively old (2015-2018) to ensure the performance is sufficient on older hardware as well.