Device fragmentation is the wide variety of devices, operating system versions, screen sizes and manufacturer customisations that a mobile app has to work on. On Android in particular, manufacturers add their own interface changes on top of the operating system.
Why it matters: It's impossible to test every combination, so fragmentation forces choices. Choosing well means focusing effort on the devices real users have, instead of spreading testing too thinly to be useful.
In practice: Teams use market share data and their own analytics to pick the devices and operating system versions that cover most of their users. They combine a small set of real devices with emulators and cloud-hosted devices, and revisit the list as the market changes.
Examples:
- Using analytics to choose the handful of devices and OS versions that cover most of an app's users.
- Finding a layout bug that only appears on one manufacturer's customised Android interface.
Common pitfalls:
- Testing only on the team's own phones, which rarely match the user base.
- Never updating the device list as new models and OS versions arrive.
How many devices should you test a mobile app on? There's no fixed number. Start with the devices and OS versions most of your users have, then add others based on risk, such as devices with known quirks.
