Testing is one of the most important phases of any development lifecycle model. The testing of the prototype types is performed on an emulator/simulator followed by testing on the real device. The emulator/simulator is often provided in the SDK. The testing on the real device, for example in the case of Android operating system development, should be performed on multiple operating system versions, multiple models of handsets with variable screen size. The test cases are documented and forwarded to the client for feedback.