Emulator vs Simulator - The Key Differences

Even before devs can start writing a single line of code, they have to figure out the breadth of project requirements, and the tools required to push, merge, build, and test code. In particular, they will need tools for rapid prototyping, mockups, and unit testing, especially in the early stages of the SDLC.

The most effective tools at this stage are virtual environments – emulators & simulators. If you’re new to software testing, you might think they are the same thing. You’d be forgiven for thinking so, because a lot of industry professionals use them synonymously.

However, they are decidedly different. Sometimes, the differences do not make much of a difference to the project in question. But, for the purpose of one’s own clarity (and future growth), knowing what distinguishes the two is foundational knowledge for every tester out there.

But let’s begin with the basic definitions.

What is an Emulator?

Emulators allows emulation – the process of mimicking a real device’s (mobile or desktop device) hard & software configuration onto a workstation. For example, Android Emulator by Android Developer Studio can mimic the features and workings of the Android OS on a tester’s desktop workstation.

Think of emulators as substitutes for an original user device. Good emulators provide (or are meant to) near-native devices capabilities & controls to reorient/adjust the device’s sensors, location, battery levels and other real-world features.

Here’s how emulators work: most computers, within devices of every size, work on something called an ISA - Instruction Set Architecture. ISA comprises machine language commands the device processor understands. Different manufacturers use their own ISAs.

The emulator’s job is to replicate the processor and feed the ISA commands from the tester’s workstation. But the ISA has to be translated to something the emulated processor understands, which is done through binary translation.

Disdvantages of using Emulators

Emulators sound pretty great, right? You get to test on any device from the comfort of your workstation, and you don’t even have to purchase or borrow all the devices you need for comprehensive testing. Well, nothing is perfect, is it? Emulators are no exception.

• Binary translation requires significant resource consumption, which leads to a fair amount of performance overhead. Android emulators almost always run much slower than real devices, which makes testing a major hassle.
• Emulators cannot replicate specific (and necessary) device conditions like network simulations & push notifications.

When to use Emulators

• When you need to verify how your software interacts with the underlying hardware & software of a 3rd-party device.
• When you need to figure out if a firmware update will cause issues within the software under test.
• When you need to test software performance in different CPUs or memory capabilities.

What is a simulator?

Note: There are no “Android simulators” out there. It is easy enough to emulate the Android OS & device configuration, so you don’t need simulators.

Simulation, like emulation, mimics a device’s environment. It replicates the behavior and configuration of the target device. It creates a virtual ecosystem that reflects how the device would work in the real world.

While this may seem similar to what emulators do, simulators don’t exactly follow the same rules. Unlike the former, simulators don’t host the hardware element of the device ecosystem. They only replicate software environments.

A major advantage of simulators, especially iOS simulators, is that they don’t require binary translation, which cuts down on performance overhead. iOS simulators will work with your native iOS workstation, replicate it’s features and show you the simulation in your Mac, iPad or iPhone.

Disadvantages of using Simulators

• The iOS simulator can only be hosted on macOS and iOS enabled devices. Since it requires Apple’s native Cocoa API to run, you either use it on a Mac or spend ages (and way too much effort) porting the simulator’s framework library to other platforms. Even if you did put in the effort, you’d probably end up with inadequate functioning and missed features.
• The simulator cannot replicate battery condition (5% vs 59% charge). In fact, it cannot replicate any device hardware.

When to use Simulators

• When you have to verify if the software under test interacts flawlessly with 3rd party applications or environments.
• When you want to verify if your software sends data to other apps as expected.
• When you want to check how your software UI renders in different screen resolutions, sizes and test environments. Sort of like preliminary responsive testing.

What Emulators & Simulators have in common

• Both tools allow you to test software within complex device environments without actually purchasing the devices. Since it takes serious effort & money to buy every device needed for comprehensive testing, these tools are seriously helpful in the early stages of development and testing.
• Since you can perform most required tests in the early SDLC stages with emulators and simulators, you get more productivity and speed from them at this point. Real device testing doesn’t become mandatory until the later stages, usually right before production.

Emulators & Simulators: Key Differences

Why Emulators & Simulators are not enough for complete software testing

As the aforementioned “Limitations” of emulators & simulators should tell you, they aren’t good enough to test software for production release. These tools cannot replicate key features, like network conditions and battery state. However, if you can’t test how your app works at 2G, chances are it will glitch when actually used in 2G.

Don’t forget that may not get accurate emulator/simulator models for older device and OS versions. In that case, you testing will only be confined to a few user devices, which means a bug will probably pop up on the devices you couldn’t test on.

On the other hand, purchasing the tens, even hundreds of devices that customers use is wildly expensive. It’s often impossible for small or mid-size organizations.

Thankfully, technology exists to overcome barriers. Platforms like Testsigma make it so that you don’t have to purchase a single device, but can test on all of them.

Testsigma is a unified, fully customizable software testing platform that works out of the box. It is designed to help teams build end-to-end tests 5X faster for web, mobile apps, & APIs. You can use Testsigma to create test scripts in plain English scripts – scripts that self-heal and require low or no maintenance.

Used by 9000+ customers to run tests worldwide (25 million tests & counting), Testsigma stands out by letting you create automation tests fast. You can write test steps in English, so it's a perfectly usable tool for non-tech personnel.

You can run tests in your local browser/device or run across 800+ browsers and 2000+ devices on our cloud-hosted test lab. You can also view step-wise results for each test and analyze real-time reports & dashboards at the individual, test suite & device levels. Moreover, Testsigma’s intelligent AI automatically fixes broken scripts, heals dynamically changing elements, and suggests fixes for test failures.