Simulators and Emulators

The team behind a running app shipped version 3.0 with a shiny new live-run tracker. It passed every test case. The map followed the route perfectly, the distance was right, the summary screen looked great. Every single test had been run on the iOS Simulator using its built-in “City Run” location.

Launch day: hundreds of one-star reviews. “Stopped recording after 10 minutes.” On real iPhones, once the screen locked, the app lost its location updates, because the background location setup was wrong. The simulator never locked, never got hot, never lost GPS signal under a bridge. It just kept feeding perfect coordinates.

The simulator wasn’t the problem. Testing only on the simulator was.

Why it matters

Nobody can own every phone. There are dozens of iPhone and iPad models and thousands of Android devices (that’s fragmentationFragmentationThe huge variety of device models, screen sizes and OS versions an app must support.Open in glossary →). Virtual devices let you test many screen sizes and OS versions for free, in seconds. But they are imitations, and you need to know exactly where the imitation ends, so the right tests happen on a real deviceReal deviceA physical phone or tablet used for testing, as opposed to an emulator or simulator.Open in glossary →.

By the end of this lesson you’ll know:

• the difference between a simulatorSimulatorSoftware that imitates a device's behavior on your computer, like Apple's iOS Simulator.Open in glossary →, an emulatorEmulatorSoftware that imitates a real device's hardware and OS on your computer, like the Android Emulator.Open in glossary → and a real device,
• how to set up and use the iOS Simulator and the Android Emulator like a tester,
• which tests you can trust on a virtual device, and which ones you can’t.

Simulator vs emulator vs real device

People use the words loosely, but there is a real difference:

• The iOS Simulator (part of Xcode, Mac only) runs your app compiled for the Mac. It imitates how iOS behaves, but it does not pretend to be iPhone hardware. That’s why it’s fast.
• The Android Emulator (part of Android Studio, on Mac, Windows and Linux) runs a complete Android system image on a virtual phone: virtual CPU, sensors, modem, battery. It runs the same APK you ship.
• A real device is a physical phone, with the real camera, GPS, radio, battery and the manufacturer’s own changes to the OS.

What each is good for

	iOS Simulator	Android Emulator	Real device
Cost and speed	Free, starts in seconds	Free, starts in under a minute	Costs money, has to be charged, updated, shared
Screen sizes and OS versions	Every current iPhone/iPad, several iOS versions	Any size, foldables, tablets, many API levels	Only the phones you own
Layout, text, translations, dark mode	Great	Great	Great
Fake location, battery, network	Location yes; battery no; network via Mac tools	Location, battery, cellular, signal: all built in	Only by really going places
Deep links, push payloads, permissions	Yes	Yes	Yes
Real performance	No (runs on the Mac’s CPU)	No (uses your computer’s CPU/GPU)	Yes
Camera	None	Virtual scene or webcam	Yes
Bluetooth, NFC, real cellular	No	Very limited	Yes
Phone calls and SMS	No	Simulated incoming call / SMS	Yes
Face ID / fingerprint	Simulated match / no match	Simulated fingerprint touch	Real sensor
Battery drain, heat, memory pressure	No	No	Yes

Simulator, emulator or real device?

The honest answer is often “start virtual, finish real”. Pick a scenario to see why:

Simulator, emulator or real device?

Pick what you need to test and see where to test it.

Push notificationsCamera scan (QR, card, receipt)Layout check on 10 screen sizesPerformance on a low-end deviceLocation-based featureFace ID / fingerprint loginPhone call interrupts the app

Recommendation

Start on the simulator/emulator, sign off on a real device

You can check the content, the tap action and the permission prompt without a phone. But the real delivery path (APNs or FCM), lock-screen behavior, Focus / Do Not Disturb and battery optimization that kills background apps only show their true colors on real hardware.

iOS Simulator

Partly

Drag an .apns file onto the window or use xcrun simctl push. Real remote push works on Apple silicon / T2 Macs with macOS 13+.

Android Emulator

Good fit

Images with Google Play or Google APIs receive real FCM pushes.

Real device

Good fit

The only way to see real delivery timing, Focus modes and vendor battery savers.

Tester tip: Test the "app killed" case: swipe the app away, send a push, then tap it. Deep-link-from-push bugs love this path.

Setting up the iOS Simulator

The Simulator comes with Xcode, which is free on the Mac App Store. You don’t need to be a developer to use it.

The menus testers use most

Menu	Item	What it’s for
Features	Face ID › Enrolled, then Matching Face / Non-matching Face	Test biometric loginBiometric authenticationUnlocking a saved login with Face ID, Touch ID or a fingerprint.Open in glossary → success, failure and fallback
Features	Location › Custom Location…, Apple, City Run, Freeway Drive	Teleport to an address or play a moving route
Features	Toggle Appearance (⇧⌘A)	Switch between light and dark modeDark modeA display setting that uses light text on dark backgrounds.Open in glossary →
Features	Toggle Increased Contrast	Check the high-contrast accessibility setting
Device	Rotate Left / Right (⌘← / ⌘→)	Test orientationOrientationWhether the device is held upright (portrait) or sideways (landscape).Open in glossary → changes and lost state
Device	Shake (⌃⌘Z)	Trigger “shake to report a bug” or “shake to undo”
Device	Home (⇧⌘H), Lock (⌘L)	Send the app to the background: an app lifecycleApp lifecycleThe states an app moves through: not running, foreground, background, suspended and terminated.Open in glossary → test
Device	Erase All Content and Settings…	A clean phone, like a fresh install
I/O	Keyboard › Toggle Software Keyboard (⌘K)	Show the on-screen keyboard (see the warning below)
File	Save Screen (⌘S), Record Screen (⌘R)	Screenshots and videos for your bug reportBug reportA clear written description of a bug so developers can reproduce and fix it.Open in glossary →
Debug	Slow Animations	Catch glitches that happen too fast to see

You can also drag files onto the Simulator window: photos and videos go to the Photos app (handy for testing an avatar upload), a .app installs, and an .apns file delivers a test push notificationPush notificationA message an app sends to the device that appears even when the app is closed.Open in glossary →.

Useful command-line tricks

Xcode includes simctl, which is great for repeatable setups. booted means “the simulator that is currently running”.

xcrun simctl list devices                                   # all simulators and their state
xcrun simctl install booted ShopApp.app                     # install a simulator build
xcrun simctl openurl booted "shopapp://product/42"          # open a deep link
xcrun simctl location booted set 52.5219,13.4132            # set GPS to Berlin
xcrun simctl push booted com.example.shopapp payload.apns   # send a test push
xcrun simctl ui booted appearance dark                      # dark mode
xcrun simctl ui booted content_size accessibility-extra-large  # very large text
xcrun simctl io booted screenshot bug.png                   # screenshot
xcrun simctl io booted recordVideo bug.mp4                  # record (Ctrl+C to stop)

Setting up the Android Emulator

The emulator comes with Android Studio, free for Mac, Windows and Linux.

Extended controls

Click the ⋮ / … (More) button on the emulator’s toolbar to open Extended controls. This is where you fake the outside world:

Panel	What you can do	Example test
Location	Set a single point, save places, play a route, import GPX/KML	Delivery zone ends at the city border
Cellular	Network type (e.g. LTE, 5G), signal strength, data and voice status, roaming	App on a weak signal or while roaming
Battery	Charge level, charger connection, battery health and status	Low-battery banner, Battery Saver behavior
Phone	Call the device from a number, send an SMS	Incoming call in the middle of checkout; SMS one-time codes
Fingerprint	“Touch” the sensor with an enrolled finger	Fingerprint login, and a non-enrolled finger failing
Camera	Use a virtual 3D room or your webcam	Camera screen opens, permission prompts
Virtual sensors	Rotate the device, change accelerometer, proximity, light	Rotation, shake, auto-brightness logic
Record and Playback	Record the screen as a video	Attach a video to a bug report

Try it yourself. Change the location, battery, network and theme and watch the delivery app react:

Extended controls playground

A food delivery app running in an Android Emulator. Fake the world around it.

14:0280%

Deliver to

Alexanderplatz

Search dishes or restaurants

Order #4821 is on the way

Live tracking · courier 1.2 km away

Near you

• CCurry CornerStreet food · 20–30 min4.6
• SSpree SushiJapanese · 25–35 min4.8
• DDöner LabTurkish · 15–25 min4.5

Location

Berlin, AlexanderplatzMunich, MarienplatzRural village (outside zone)No GPS fix / location off

Lat, long: 52.5219, 13.4132

Battery

Charge level80%ChargerNoneAC charger

Cellular / network

Wi-Fi5GLTE3G (slow)Airplane mode

Display

Dark theme

Change a control on the right. Each one is a real setting in the emulator's Extended controls (the "…" button on its toolbar).

Installing builds

iOS SimulatorAndroid Emulator

• Drag a .app onto the Simulator window, or run xcrun simctl install booted ShopApp.app.
• The build must be made for the simulator. An .ipa file or a TestFlightTestFlightApple's service for distributing beta builds of iOS apps to testers before App Store release.Open in glossary → build is made for real iPhones and won’t install on the Simulator. Ask the developers for a simulator build (or run it from Xcode).
• To start fresh, delete the app (long-press its icon, like on a phone) or use Device › Erase All Content and Settings…

• Drag an .apk onto the emulator window, or run adb install app.apk (see adb basics).
• The same APK works on emulators and real phones, as long as it includes code for the emulator’s processor type. Most apps do.
• An .aab (Android App Bundle) is meant for Google Play and can’t be dragged in directly. Ask for an APK, or install through Google Play internal testing or Firebase App DistributionFirebase App DistributionGoogle's service for sending pre-release Android (and iOS) builds to testers.Open in glossary →.
• To start fresh: Settings › Apps › the app › Storage › Clear storage, or Wipe Data for the whole virtual device in the Device Manager.

Useful toggles for testers

These settings find a surprising number of bugs. All of them work on virtual devices:

What	iOS Simulator	Android Emulator
Dark mode	Features › Toggle Appearance (⇧⌘A)	Quick Settings tile, or Settings › Display (Display & touch on newer versions) › Dark theme
Large text	Settings › Accessibility › Display & Text Size › Larger Text, or Xcode’s Environment Overrides while running	Settings › Display › Display size and text (font size)
Language and region	Settings › General › Language & Region, or the scheme’s App Language in Xcode	Settings › System › Languages
Rotation	Device › Rotate Left / Right	Rotate buttons on the emulator toolbar
Location	Features › Location	Extended controls › Location

Large textDynamic TypeThe phone setting that lets users make text bigger or smaller across apps.Open in glossary → and long languages (German, Finnish) are the fastest way to find truncationTruncationText that gets cut off because it doesn't fit its space.Open in glossary → bugs. Changing the localeLocaleRegional settings that control language and formats for dates, numbers and currency.Open in glossary → also changes date, number and currency formats, so check prices and dates while you’re at it.

What to test where

Safe to test on simulators and emulators

• Layout on every screen size, including the smallest supported phone, tablets and foldables, and the safe areaSafe areaThe part of the screen not covered by the notch, Dynamic Island, rounded corners or home indicator.Open in glossary → around notches.
• Flows and logic: sign-up, search, cart, settings, error messages.
• System settings: dark mode, large text, languages, rotation.
• Fake-able conditions: GPS location and routes, battery level (Android), network type, permissions granted or denied.
• Entry points: deep linksDeep linkA link that opens a specific screen inside an app instead of just its home screen.Open in glossary →, push payloads, opening the app from a share sheet.

Needs a real device

• Hardware: camera, Bluetooth accessories, NFC payments, real biometrics, haptics.
• Performance: start-up time, scrolling, animations, memory on low-end phones.
• The physical world: real GPS outdoors, weak signal, switching between Wi-Fi and mobile data, battery drain and heat.
• Real interruptionsInterruptionAnything that takes the user away from the app mid-task: a call, an alarm, a notification, low battery.Open in glossary →: phone calls (always on iPhone), alarms, low-power mode, the OS killing the app in the background.
• Manufacturer quirks: Samsung, Xiaomi and others change Android, especially battery savers that kill background work and notifications.

Bugs that slip through when you only test virtually

#	Bug	What you see	Typical severity
1	Background tracking stops	Run or delivery tracking freezes when the screen locks on real phones	High
2	Keyboard covers the button	On the Simulator the hardware keyboard hid the on-screen one; on a phone you can’t reach Pay	High
3	Janky scrolling	Smooth on the emulator, stuttering on a budget phone with 3 GB RAM	Medium
4	Camera screen crashes or stays black	The scanner was never exercised because the Simulator has no camera	High
5	Push never arrives	Works with drag-and-drop payloads, but the real server uses the wrong APNs environment	High
6	Killed by battery saver	Reminders or uploads silently stop on some Android brands	Medium
7	State lost after background kill	Real phones with little memory kill the app; the cart or form is empty on return	Medium
8	Breaks on network switch	Upload fails when walking out of Wi-Fi onto mobile data	Medium

Practice: where would you test it?

You’re planning testing for a shopping and fitness app with three emulators, two simulators and two real phones. Sort each idea into the right place:

Sort the test ideas

Is a simulator/emulator enough, or do you need a real device?

0/10 Reset

1. 01Check the checkout screen layout on iPhone SE, iPhone 16 Pro Max and iPad.

   Sim / emulatorReal device

2. 02Scan the QR code printed on a paper receipt to collect loyalty points.

   Sim / emulatorReal device

3. 03Check that the "Low battery: tracking paused" banner appears at 10% on Android.

   Sim / emulatorReal device

4. 04Check that scrolling the product feed stays smooth on a 3-year-old budget Android.

   Sim / emulatorReal device

5. 05Look for truncated labels in the German translation.

   Sim / emulatorReal device

6. 06Pair the fitness app with a heart-rate chest strap over Bluetooth.

   Sim / emulatorReal device

7. 07Check every screen in dark mode for unreadable text.

   Sim / emulatorReal device

8. 08Check that the link shopapp://product/42 opens the right product page.

   Sim / emulatorReal device

9. 09Track a 45-minute outdoor run with GPS and check battery drain.

   Sim / emulatorReal device

10. 10Receive a phone call on an iPhone while a payment is processing.

    Sim / emulatorReal device

Cloud device farms

When you need a phone you don’t own (a specific Samsung model, an old iPhone, a tablet), a cloud device farm rents you real devices through the browser. You install the build, tap around remotely, and record videos and logs.

Common options are BrowserStack, Sauce Labs, LambdaTest, AWS Device Farm and Firebase Test Lab (the last two are aimed mostly at automated tests). They’re great for reproducing a bug a user reported on “Galaxy A14, Android 14”, but there is some lag, and you can’t hold the device, walk outside or plug in a Bluetooth gadget.

Example test cases

Checklist

Simulator and emulator testing checklist

0 of 11 checked

Copy

• I know which build I need: a simulator build (.app) for iOS, an APK for Android
• Layout is checked on the smallest and largest supported screens, plus a tablet
• The oldest and newest supported OS versions are covered
• Forms are tested with the software keyboard visible
• Dark mode, the largest text size and a long language are checked
• Rotation and background/foreground do not lose data
• Location-based features are tested with several places and "location off"
• Battery and network conditions are faked on the emulator
• Hardware features (camera, Bluetooth, NFC, biometrics) are signed off on real devices
• Performance is checked on a real low-end phone
• Push notifications and calls are verified on real devices before release

Check your understanding

Quick quiz

0/5 answered · 0 correct

1. 1.What is the main technical difference between the iOS Simulator and the Android Emulator?

   AThe Simulator is paid, the Emulator is freeBThe Simulator runs the app compiled for the Mac; the Emulator runs a full Android system image on virtual hardwareCThe Simulator only supports iPadsDThere is no difference

2. 2.You must test how a budget Android phone handles a long product feed. Where should you test?

   AAndroid Emulator with less RAMBiOS SimulatorCA real low-end Android phoneDAny of them, results are the same

3. 3.Which test can the Android Emulator do but the iOS Simulator cannot?

   ADark modeBSimulate an incoming phone callCChange the screen sizeDOpen a deep link

4. 4.A developer sends you a TestFlight link. Can you test that build on the iOS Simulator?

   AYes, drag it inBNo, TestFlight builds are for real devices; you need a simulator buildCOnly with Face ID enabledDOnly on iPad simulators

5. 5.Forms look perfect on the Simulator, but users say the keyboard hides the Pay button. What probably went wrong in testing?

   AThe tester used dark modeBThe software keyboard was hidden because the Mac keyboard was connectedCThe app was not installedDThe location was wrong

Key takeaways

• The iOS Simulator imitates iOS on your Mac; the Android Emulator emulates a full virtual phone. Neither is a real device.
• Use virtual devices for layout, flows, settings and fake-able conditions: screen sizes, OS versions, dark mode, large text, languages, location, battery, network.
• Use real devices for hardware, performance, the physical world, real interruptions and the final sign-off.
• Know the menus: Features and Device on the Simulator, Extended controls on the Emulator.
• Fill the gaps with a small real-device lab and a cloud device farm.