Emulator testing is a software-defined environment designed to mimic the hardware and software conditions of an actual mobile device, providing a way to run applications for testing purposes within an environment that is identical in theory to the real-world environment. Emulators save time by not requiring physical devices, making it easy to test on a range of different types of mobile environments. However, emulator environments may not perfectly mirror actual mobile devices and can yield different results from tests run on real devices. Emulator testing is typically most useful early in the software testing process, but should be followed by real-device testing to achieve broad device coverage and confidence that code will run as required in production. Real-device testing provides a second line of defense to plug gaps in emulator testing and should be performed judiciously, focusing on relevant devices and configurations for the target market and user. In some cases, it can make sense to perform real-device testing at the same time as emulator testing, especially when trying to achieve fast release velocity or when emulators fail to mimic certain types of devices or configurations.