Use your analytics to build a device and OS matrix that covers 80-90% of your users. Test critical flows on real devices and use emulators for broader coverage. Always test on the oldest supported OS version.
Strong answers cover: device fragmentation, OS version coverage, network condition testing (3G, offline), battery and performance impact, gesture and touch interactions, push notifications, app permissions, and the choice between real devices and emulators. Best candidates discuss a pragmatic device matrix based on analytics data rather than testing every device.
Important for teams with mobile products. Candidates who only test on the latest iPhone miss the reality of device fragmentation. Those with practical mobile testing experience know the pain points and workarounds.