Emulators and simulators are often free of charge, and so can prove a useful and economical addition to your test routine. It is important, however, to understand the differences between an emulator and a simulator.

Emulators

An emulator is a piece of software “that translates compiled code from an original architecture to the platform where it is running” (see “Programming the Mobile Web.” O’Reilly, 2010). Emulator’s don’t simply simulate a device’s operating system; they provide a means to run a virtual version of it on your computer (often down to the specific version number). Emulators therefore provide a useful and accurate environment to test and debug your mobile app.

Pros

• Emulators reflect the true web browser (and operating system) environment, so are ideal for testing and debugging visual design, overall rendering, and the execution of simple client-side interactions.
• Many emulators are provided free of charge by the OEM or platform manufacturer.

Cons

• Emulators cannot provide emulation of individual devices from a hardware and CPU point of view. They cannot reveal, for example, that animations will perform poorly due to limited CPU power, or that link buttons will not respond as expected due to poor screen touch sensitivity.
• Likewise, emulators may not represent real-world conditions such as network latency, limited bandwidth, or determining the device’s location.
• Emulators are typically bundled into an operating system SDK and they can take considerable time to install and learn to use correctly. They also require regular updates to ensure they always include the most up-to-date operating system versions.
• Most emulators do not work with automation tools and so must be used manually. The user agent strings provided by emulators often differ from those of the actual devices. Logic that relies on specific user agent strings may not behave as expected on emulators.

Simulators

A simulator is a far less sophisticated tool that is only designed to provide a reasonable facsimile of the experience on a device. Simulators vary greatly in their ability to represent the true device environment. Some, such as the iOS simulator, provide an excellent facsimile of the overall environment, including simulation of the native iOS font. Others may simply simulate the screen size of popular devices.

Pros

• Most (but not all) simulators are provided free of charge by the OEM or platform manufacturer.

Cons

• Simulators cannot emulate the actual operating system, or web browser found on the device, so they cannot be relied on to test or debug front-end design or functionality (the excellent iOS simulator is an exception and provides an excellent browser simulator).
• Similar to emulators, simulators will not reflect differences in device hardware, performance, CPU, fonts, color gamut, display density, network speed.