There are several standards for mobile data connections (edge, umts, 3G, 4G) as well as for wifi (b, g, n). Sometimes there might be no connection available at all or the device is in flight mode.

1. Screen sizes. The Android world is not simple. The variety of different aspect ratios and pixel densities can be overwhelming. With the launch of iPhone 6, Apple brings new screen sizes to the iOS world as well. Though iOS developers are used to pixel perfect screen design, they now need to change their mindset to the adaptive screen design instead. For testing it means that we need to check on various devices that all the necessary screen elements are accessible with different screen sizes and aspect ratios.
2. Connection types. There are several standards for mobile data connections (edge, umts, 3G, 4G) as well as for wifi (b, g, n). Sometimes there might be no connection available at all or the device is in flight mode. When users move around the connection type might change. Unfortunately some carriers filter the web on their own will, which results in the devices being connected without actually having connection with a specific service (messaging or calling through apps). Even though connection API’s on mobile platforms have been developed keeping those challenges in mind, the real world environment is still very much varying and interesting set of issues may occur. It’s important to test the bandwidth usage as not all carriers are supporting unlimited data volumes.
3. Different OS versions. iOS users are known to be upgrading quickly to the newest versions (iOS 8.0 uptake has been around 50% during first two weeks). On the contrary, Android uptake has historically been very slow and the fragmentation is wide. This means that app developers need to support older OS versions and older API’s, and testers need to test for those.
4. Power consumption and battery life. The innovation in the battery storage capacity field hasn’t been as quick as in the app consumption. We are running lots of apps during the day and several processes are running on background without us even noticing. This all requires cpu cycles which on it’s turn require power and thus the batteries tend to dry. When testing mobile apps we need to make sure that the power consumption is kept minimal and the app is developed by keeping the best practices in mind.
5. Usability. Mobile device screens are relatively small and there are always more data we would like to present than possible to fit to the screen. It’s challenging to keep the interaction clean and simple for the user, and at the same time display all the necessary information. Font size and readability are other challenging factors of usability. When testing mobile apps it’s important to pay attention to the size of click areas and making sure that all texts are readable without lenses.
6. Internationalisation. Most of the apps are designed to be used on international markets. Testing for translation is only one piece of the whole internationalisation testing. Testers should also take into account regional traits (locale settings, timezones) and target audience. Changing time while app is running might cause some interesting artefacts. Also some designs that are working in the western world might not work in the east and vice-versa. Right-to-left languages have always kept developers puzzled.