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Use Google’s Desktop Head Unit Emulator (DHU) to test Android Auto layouts on a development computer, then verify the same build in at least one real vehicle before release. Create a matrix that varies the DHU’s resolution, aspect-ratio margins, DPI, content insets, frame rate and control mode. Test touch, rotary and hybrid interaction separately, record clipping and focus behavior, and run the applicable category quality checks. The DHU is for Android Auto projection from a phone; Android Automotive OS emulator profiles are a separate platform and must be tested separately.
What screen-size testing must prove
An Android Auto app is rendered for a car display whose usable shape and controls vary by vehicle. A screen can be wider, taller, denser or partially letterboxed than the configuration used during development. A layout that looks correct at one resolution may clip text, truncate buttons, waste space or make rotary focus difficult on another.
The practical goal is not to test every model of vehicle. It is to demonstrate that your app remains readable, navigable and category-compliant across a deliberate range of display and input conditions, and then to confirm those findings on hardware. Google’s Desktop Head Unit documentation describes the DHU as the desktop emulator for Android Auto, while the broader car-app testing guide requires real-vehicle user-experience validation before submission.
Install and connect the Desktop Head Unit Emulator
Prepare the development environment
The DHU runs on Windows, macOS and Linux. Install Android Studio and an Android Auto-compatible test phone. The phone needs your app installed, along with the Android Auto application supported by your test setup. Keep the phone unlocked and use a build variant that can be distributed to your testers.
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- Open Android Studio and choose Tools > SDK Manager.
- Select the SDK Tools tab.
- Enable the Android Auto Desktop Head Unit Emulator package and apply the installation.
- Build and install your Android Auto app on the supported Android phone.
- Connect the phone to the development computer using a supported USB data connection, or prepare ADB tunneling as described in Google’s DHU instructions.
Google documents both USB accessory mode and ADB tunneling as connection options. Use one method consistently in a test run so a connection change is not mistaken for an app defect. If you use Linux, check the current DHU 2.x instructions for the required GLIBC level and additional libraries before troubleshooting your app; missing host dependencies can prevent the emulator from starting.
Start a known-good baseline
Launch the DHU using the installation and sample configuration supplied with the SDK. Confirm that the phone establishes an Android Auto session and that a known-good app can be opened. Record the DHU version, host operating system, phone model and Android Auto version with the test build. This baseline makes later failures reproducible instead of leaving you to guess whether a display problem is caused by the app, phone or host.
Build a display-configuration matrix
The DHU accepts configuration files that control video resolution, DPI, frame rate, margins and content insets. Google’s documented Android Auto video presets are the following:
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|---|---|---|
| 800 × 480 | Small baseline display | Default documented Android Auto video resolution |
| 1280 × 720 | HD landscape display | Supported DHU resolution |
| 1920 × 1080 | Full-HD landscape display | Supported DHU resolution |
| 1280 × 720 with 280 px width and 120 px height margins | Approximate a 1000 × 600 visible area | Produces 140 px on each side and 60 px above and below in Google’s example |
| 800 × 480 with 50 px width and 30 px height margins | Approximate a 750 × 450 visible area | Google’s documented margin example |
These values are supported video configurations, not measurements of how many vehicles use each size. The resolution and margin settings are documented in Configure the DHU. Start with the SDK’s sample configuration files and change one variable at a time when diagnosing a defect.
Cover aspect ratios with margins
A vehicle may expose a visible area that does not match a 16:9 preset. Rather than treating every shape as a new resolution, choose the nearest supported video size and add horizontal or vertical margins to model pillarboxing or letterboxing. Test both the full frame and the reduced content area. Look for text wrapping, cards that become too narrow, controls anchored to the wrong edge and artwork that is cropped instead of scaled.
When reporting a failure, state the base resolution and the exact width and height margins. “Fails on a wide screen” is not reproducible; “1280 × 720 with 280 px width and 120 px height margins clips the trailing label” is.
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Vary DPI and content insets
Resolution describes available pixels; DPI changes the apparent size of UI elements. Two configurations with the same pixel dimensions can present different effective text and control sizes. Content insets change the space available to your app inside the display frame. Include at least one lower-density and one higher-density case that your app is expected to support, and test insets large enough to expose assumptions about edge-to-edge content.
Capture screenshots at every DPI and inset combination. A screenshot alone is insufficient: note whether the issue is visual scaling, a reduced safe area, or an interaction target that moved. For general principles on exercising different Android display and window sizes, see Google’s screen and window-size testing guidance.
Include frame rate when timing matters
If your app has animated transitions, scrolling or progress indicators, include the frame-rate setting in the configuration record. A layout defect can be hidden by a smooth animation, while a timing or focus defect can appear only when frames are delivered differently. Treat frame rate as a test dimension, not an informal emulator preference.
Configure and document each DHU case
Create a small, version-controlled collection of configuration files rather than editing one file repeatedly without a record. Name each file for the dimensions it changes, such as a preset resolution, margin profile, DPI and input mode. Keep the original sample files unchanged so you can return to a known baseline.
- Copy the relevant DHU sample configuration into your test-config directory.
- Set the documented video resolution.
- Add width and height margins for the target aspect ratio, if needed.
- Set the intended DPI, frame rate and content insets.
- Run the app and verify that the DHU reports the expected connection and display state.
- Save the configuration name and a screenshot with the test result.
Do not change resolution, DPI, margins and app state simultaneously while investigating a defect. First reproduce it with one changed variable; then add the other dimensions to determine whether the problem is a threshold effect or a general layout failure.
Test touch, rotary and hybrid control layouts
Pixels are only half of the car experience. The DHU supports touch, rotary and hybrid input. A touch pass can succeed while a rotary pass leaves the user unable to reach a button, traps focus in a card or makes back navigation ambiguous.
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Touch mode
- Tap every primary action, list item, tab and dismiss control.
- Check that touch targets remain visible and do not overlap after margins or insets reduce the usable area.
- Repeat actions after rotation-like state changes in the app, such as opening a detail page and returning to a list.
- Verify that scrolling does not hide the only route to a required action.
Rotary mode
In rotary mode, DHU mouse clicks are ignored. Keyboard controls simulate rotary operations, so use the documented keyboard mapping for rotation, selection and back navigation. Exercise the complete focus order: enter the screen, rotate through every actionable element, select an item, open a secondary screen, and return. Record any element that cannot receive focus, receives focus in an unsafe order, or appears selected without a visible indication.
Hybrid mode
Hybrid control combines touch and rotary behavior. Switch between the two interaction styles during one task instead of resetting the app after each action. This exposes state bugs in which a touch tap changes the visual selection but the rotary controller still points to a previous element.
The presence of a DHU input mode does not prove that every vehicle manufacturer implements its controller identically. Treat the emulator as a repeatable interaction approximation, not as a certification of every OEM control scheme.
Use a repeatable test workflow
- Define the supported scope. List the app category, minimum Android and Android Auto versions, phone builds, planned vehicle types and the display cases you will exercise.
- Prepare the build. Install the same signed or debug build that testers will receive. Record the commit, version name and version code.
- Connect the phone. Establish USB accessory mode or ADB tunneling and verify the Android Auto session before opening the app.
- Run the baseline. Use 800 × 480 with the default configuration. Confirm that navigation, rendering and audio or communication behavior relevant to your category work.
- Change display shape. Run 1280 × 720 and 1920 × 1080, then apply margin profiles such as the documented 1000 × 600 and 750 × 450 approximations.
- Change density and safe area. Apply the planned DPI and content-inset cases without changing the app build.
- Repeat each task by input mode. Complete the touch, rotary and hybrid passes separately; do not infer rotary success from touch success.
- Exercise app states. Test first launch, empty data, populated data, long labels, errors, loading, permission prompts, return-from-background and deep links that your category supports.
- Record evidence. For each case, save the configuration filename, resolution, margins, DPI, frame rate, insets, input mode, app state, observed clipping or truncation, focus or selection behavior, and whether the issue reproduced on a second run.
- Retest fixes across the matrix. A change that repairs a narrow layout can break a wide one. Re-run the baseline and every case that exercises the modified component.
Maintain a test-matrix record
A shared table keeps failures comparable across developers and QA members. Use one row per configuration and avoid broad labels such as “small screen.”
| Field | What to record |
|---|---|
| Platform | Android Auto DHU, or Android Automotive OS emulator when that platform is explicitly in scope |
| Display | Base resolution, aspect-ratio margins and resulting visible area |
| Density | DPI value and any density-dependent observation |
| Safe area | Content insets and the affected edge |
| Motion | Frame-rate setting when animations or scrolling are relevant |
| Input | Touch, rotary or hybrid |
| App state | Screen, data condition, navigation history and interruption state |
| Result | Clipping, truncation, overlap, focus order, selection visibility and reproduction count |
| Evidence | Screenshot, configuration file and build identifier |
This record is a QA practice derived from the DHU’s configurable controls and Google’s testing guidance; it is not a claim that Google prescribes this exact table. Its value is traceability: another tester can recreate the same dimensions and determine whether a fix changed the result.
Keep Android Auto separate from Android Automotive OS
Android Auto is a projection experience: the app runs on a phone and is presented through a compatible vehicle or head unit. The DHU emulates that Android Auto head unit connection.
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Android Automotive OS is an operating system built into the vehicle. Google’s Automotive OS emulator documentation describes vehicle system images and hardware profiles for landscape, portrait and ultrawide displays, including custom profiles for configurations not covered by the supplied profiles.
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|---|---|---|
| Where does the app run? | On the connected Android phone and project to the emulated head unit | Inside the Automotive OS vehicle system image |
| What does the display configuration represent? | Android Auto video resolution, DPI, margins, insets and input mode | Vehicle hardware profile and system-image display shape |
| Which shapes are emphasized? | Documented DHU video presets plus margin-based approximations | Landscape, portrait, ultrawide and custom hardware profiles |
| Can one replace the other? | No | No |
Do not report an Automotive OS portrait profile as an Android Auto head-unit configuration. If your product targets both platforms, maintain separate test plans, builds or feature checks as required by each platform’s APIs and quality rules.
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Clipped or truncated content
Reproduce the issue at the smallest supported preset, then at the same preset with margins. If clipping begins only after margins are added, inspect assumptions about the full frame and apply the content insets to layout calculations. If it appears at every size, check fixed widths, minimum sizes and text that cannot wrap.
Unexpected empty bands
Confirm whether the bands are intentional margins or an incorrectly applied inset. Compare the configuration file with the screenshot and verify that width and height margins were not swapped. The 1000 × 600 example uses 280 px of total width margin and 120 px of total height margin on a 1280 × 720 base; preserve those dimensions when reproducing the example.
Rotary selection appears stuck
Make sure the DHU is actually in rotary mode, where mouse clicks are ignored, and use the keyboard controls for rotation and selection. Then inspect focus order and ensure every actionable element has a visible selected state. Repeat after returning from a detail screen, because stale focus is often state-dependent.
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The DHU will not start on Linux
Separate host setup from app debugging. Check the current Android Developers DHU instructions for the required GLIBC version and additional libraries, then validate the emulator with a known-good app before filing an app issue.
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The emulator passes but a vehicle fails
Compare the real vehicle’s visible area, controller, software version and connection path with the DHU case. A DHU pass covers only the dimensions and controls you configured; it cannot establish that every OEM controller, touch implementation or system overlay behaves the same way.
Validate in a real vehicle before release
Google recommends testing the app’s user experience in real vehicles before submission. Plan at least one pass on the environments available to your team, using an Android Auto-compatible head unit or vehicle when possible. Describe the sample accurately: one vehicle validates that vehicle and software combination, not the entire installed base.
Distribute candidate builds through a trusted testing route so the vehicle pass uses the intended artifact. Google’s car testing guidance identifies Internal App Sharing and an Internal Test Track as options for installing builds without waiting for ordinary Play review. Keep the build identifier in your vehicle test record and remove test-only data before wider release.
Review category-specific car quality
Before submission, read the current Car app quality requirements for your category. Navigation, media, messaging and other categories have different expectations for distraction, navigation, templates, actions and behavior while driving. Check every criterion that applies to the final app, not only the screen-size cases that passed in the DHU. Google’s quality pages can change, so recheck the criteria and tool requirements at release time.
When the matrix is complete
You have adequate emulator coverage when each planned display case has a named configuration, each input mode has completed tasks, failures have reproducible evidence, and fixes have been retested against the affected dimensions. You have release evidence only after that matrix is paired with a real-vehicle pass and the category checklist. The DHU makes variation fast and repeatable; hardware testing confirms the parts of the car experience that an emulator cannot model.
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