Testing, Performance and Play Store Interview Questions for Android App Development

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Local unit tests on the JVM cover ViewModels, use cases, repositories and mappers with JUnit, fakes and coroutine test tools; they are fast and most numerous. Instrumented tests run on a device or emulator for Room, Compose UI and integration flows. End-to-end UI tests check critical journeys like login and checkout. Screenshot tests catch visual regressions. Follow the testing pyramid: many unit tests, fewer UI tests.

What is an ANR and how do you prevent it?

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An ANR (Application Not Responding) happens when the main thread is blocked, for example an input event not handled within about 5 seconds or a BroadcastReceiver taking too long. Causes include disk or network work on the main thread, heavy computation, lock contention and slow SharedPreferences commits. Prevent ANRs by moving work to background dispatchers, using StrictMode in debug builds, and tracking ANR rates in Android vitals.

What is an Android App Bundle and why does Play require it?

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An App Bundle (.aab) is a publishing format containing all compiled code and resources. The Play Store generates optimised APKs for each device configuration, delivering only the needed screen density, CPU architecture and language resources, which reduces download size. Since August 2021, new apps on Play must use AAB with Play App Signing, where the store holds the app signing key and you sign uploads with an upload key.

Explain the steps to publish an app on the Play Store.

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Create a developer account, then an app in Play Console. Complete the store listing, content rating, data safety form, target audience, privacy policy and permissions declarations. Build a signed release AAB with a higher versionCode, upload it to internal testing first, then closed or open testing, and finally production with a staged rollout. New personal accounts must run a closed test with at least 12 testers for 14 days before production.

Tell me about an app or feature you are proud of building.

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Choose something with clear impact. For example: I built the offline cart for our grocery app. Users in low network areas could add items without connection, and the cart synced later with conflict handling. I used Room, WorkManager and a sync status field, and wrote migration and sync tests. After release, cart abandonment from network errors dropped noticeably, and the pattern was reused for the wishlist feature.

Where do you see yourself in five years as an Android developer?

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Keep it genuine and tied to growth. For example: in five years I want to be a senior or lead Android engineer who owns the architecture of a large app, mentors juniors and works closely with product on decisions. I plan to deepen my skills in performance, Compose and Kotlin Multiplatform, and contribute to the team's engineering practices. I hope to grow that path in a company like this one.

How do you handle a code review comment you disagree with?

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I first assume the reviewer has a reason and ask questions to understand it. If I still disagree, I explain my reasoning with evidence, such as documentation, a benchmark or a test, and suggest a short call if comments go back and forth. If it is a matter of preference, I follow the team convention. The goal is the best code for the team, not winning the argument.

Write a unit test for a ViewModel using a fake repository and runTest.

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class ProductViewModelTest { @get:Rule val mainRule = MainDispatcherRule() @Test fun loadsProductsIntoState() = runTest { val fake = FakeProductRepository(listOf(Product("1", "Pen", 10.0))) val vm = ProductViewModel(fake) advanceUntilIdle() val state = vm.state.value assertFalse(state.loading) assertEquals(1, state.items.size) assertNull(state.error) } }

How do you find and fix memory leaks in an Android app?

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Add LeakCanary to debug builds; it detects retained Activities, Fragments and ViewModels and shows the reference chain. Common leaks are static or singleton references to Context or Views, listeners not unregistered, inner classes holding Activity references, and Fragment view bindings not cleared in onDestroyView. Fix by using application context, lifecycle-aware components and weak references only where needed. Confirm with Memory Profiler heap dumps.

What does R8 do in a release build?

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R8 shrinks code by removing unused classes and members, optimises bytecode by inlining and removing dead branches, obfuscates names to make reverse engineering harder and reduce size, and shrinks resources when enabled. It needs keep rules for code accessed by reflection, such as some serialization or SDK classes. Upload the mapping file to Play Console and Crashlytics so obfuscated stack traces can be decoded.

What is targetSdkVersion and why does Play enforce updates?

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targetSdkVersion tells Android which platform behaviour your app was tested against; the system applies newer behaviour changes only when you target that level. The Play Store requires new apps and updates to target a recent API level, usually within one year of a release, so users benefit from security and privacy changes. minSdk sets the oldest supported version and compileSdk the API you compile against.

Write a Gradle configuration for release signing and minification using environment variables.

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android { signingConfigs { create("release") { storeFile = file(System.getenv("KEYSTORE_PATH") ?: "release.jks") storePassword = System.getenv("KEYSTORE_PASSWORD") keyAlias = System.getenv("KEY_ALIAS") keyPassword = System.getenv("KEY_PASSWORD") } } buildTypes { release { isMinifyEnabled = true isShrinkResources = true proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro") signingConfig = signingConfigs.getByName("release") } } }

How do you set up CI/CD for an Android app?

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On every pull request, run lint, ktlint or detekt, unit tests and a debug build in a CI service like GitHub Actions or Bitrise, with Gradle caching. On merge to main, build a signed release AAB using secrets, run instrumented tests on emulators or a device farm, and upload to the Play internal track with Gradle Play Publisher or fastlane. Promote to production manually after QA with a staged rollout.

The crash-free rate dropped after a release only on Android 15 devices. How do you respond?

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Halt the staged rollout immediately. Filter Crashlytics or Play vitals by OS version to find the top crash, then check Android 15 behaviour changes such as edge-to-edge enforcement, foreground service rules or new restrictions affecting your target SDK. Reproduce on an Android 15 emulator, fix, add a test, and resume rollout with the hotfix. Afterward, add Android 15 devices to the regular test matrix.

The Play Store rejected your update for a policy violation about permissions. What do you do?

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Read the rejection email and policy centre message carefully to see which permission or declaration failed, often SMS, call log, background location, all-files access or exact alarms. Remove the permission if a less sensitive alternative exists, such as the SMS Retriever API or photo picker. Otherwise update the permission declaration form with a clear use case and video. Check the merged manifest for permissions added by libraries.

The APK size grew to 120 MB and installs from small towns are dropping. How do you reduce it?

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Analyse the build with APK Analyzer. Publish as an App Bundle so users get only their density, language and ABI. Enable R8 and resource shrinking, convert images to WebP or vectors, remove unused libraries and duplicate dependencies, and move large optional features or assets to Play Feature Delivery or Play Asset Delivery. Avoid bundling all native libraries for every ABI. Track size in CI.

QA says a bug happens only on one manufacturer's phones. How do you debug it?

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Get exact device model, OS and skin versions, and steps. Use a remote device lab or Firebase Test Lab to reproduce if you lack the device. Collect logcat and bug reports, and compare behaviour around known differences like battery optimisation, autostart restrictions, custom permission dialogs or WebView versions. Add targeted logging or a non-fatal Crashlytics event, then apply a fix guarded by checks only if necessary.

The app's cold start takes 4 seconds. How do you improve it?

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Measure first with Macrobenchmark StartupTimingMetric on a release build. Then reduce work in Application.onCreate by deferring SDK initialisation, using App Startup or lazy injection, and moving disk I/O off the main thread. Simplify the first screen, avoid blocking on network before showing UI, use the SplashScreen API properly, and add a Baseline Profile, which often improves startup by about 20 to 30 percent.

What are Baseline Profiles?

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A Baseline Profile is a list of classes and methods used in critical journeys like startup and scrolling, shipped with the app. The Android Runtime uses it to compile that code ahead of time on install, avoiding slow interpretation and JIT on first runs. You generate it with the Baseline Profile Gradle plugin and Macrobenchmark tests. Compose and many Jetpack libraries ship their own profiles, but an app-specific one gives larger gains.

Your banking app must pass a security audit. What would you check on the Android side?

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Check secure storage with Keystore and no secrets in code, TLS only with pinning where justified, no sensitive data in logs, FLAG_SECURE on sensitive screens, root and tamper checks using Play Integrity, exported components reviewed, WebView with JavaScript bridges restricted, R8 obfuscation, session timeout, and biometric authentication with BiometricPrompt and CryptoObject. Use the OWASP MASVS as the checklist and fix findings by severity.

How would you roll out a risky new feature to millions of users safely?

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Ship it behind a remote feature flag defaulted off, release the build with a staged rollout and monitor crash-free and ANR rates. Then enable the flag for internal users, then 1, 5, 25 and 100 percent, watching business metrics and errors at each step. Keep a kill switch ready, define rollback criteria beforehand, and keep the old path until the new one is stable.

Users report battery drain after the latest update. How do you investigate?

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Check Android vitals for excessive wake locks and wakeups, then use Battery Historian or the Energy Profiler to look at wake locks, alarms, location requests, jobs and network activity. Common causes are frequent location updates, a foreground service left running, polling instead of push, and WorkManager jobs scheduled too often. Fix by batching work, using lower location priority, stopping services promptly and adding proper constraints.

Your app has 60 Gradle modules and builds take 15 minutes. How would you speed them up?

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Profile with Gradle build scans to find slow tasks. Enable the configuration cache and build cache, including a remote cache in CI. Use KSP instead of kapt, avoid unnecessary api dependencies so changes do not recompile many modules, use convention plugins, and keep non-transitive R classes. Check heavy annotation processors and give Gradle enough memory. Developers can build only the module they work on with a sample app.

How do you measure app quality after release?

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Track crash-free users and ANR rate in Play vitals and Crashlytics, keeping them below Play's bad behaviour thresholds of 1.09 percent user-perceived crash rate and 0.47 percent ANR rate. Monitor startup time, slow and frozen frames, network error rates and key funnel metrics like login success. Read Play reviews and ratings by version. Set alerts and review these numbers in every release meeting.

Describe a time you improved app performance with measurable results.