A method for testing operation of a computer application. An emulator is provided to run on a development platform subject to limitations of multiple different target devices, the emulator including a set of emulator APIs corresponding to target Application Program Interfaces (APIs) available on the different target devices. A subset of the target APIs that are supported by one of the target devices is specified. Access by the emulator to the emulator APIs that correspond to one or more of the target APIs that are not in the specified subset is blocked. The application is run on the emulator subject to the blocked access.