Use this skill when writing or configuring mobile app tests with Detox or Appium, setting up device farms (AWS Device Farm, Firebase Test Lab, BrowserStack), integrating crash reporting (Crashlytics, Sentry, Bugsnag), or distributing beta builds (TestFlight, Firebase App Distribution, App Center). Triggers on mobile e2e testing, native app automation, device matrix testing, crash symbolication, and OTA beta distribution workflows.
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Use this skill when writing or configuring mobile app tests with Detox or Appium, setting up device farms (AWS Device Farm, Firebase Test Lab, BrowserStack), integrating crash reporting (Crashlytics, Sentry, Bugsnag), or distributing beta builds (TestFlight, Firebase App Distribution, App Center). Triggers on mobile e2e testing, native app automation, device matrix testing, crash symbolication, and OTA beta distribution workflows.
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Mobile Testing
Mobile testing covers the end-to-end quality pipeline for native and hybrid mobile
applications - from writing automated UI tests with Detox and Appium, to running them
across real device farms, to capturing crashes in production and distributing beta builds
for human verification. Unlike web testing, mobile testing must deal with platform
fragmentation (iOS/Android), device-specific behavior, app lifecycle events, permissions
dialogs, and binary distribution gatekeeping by Apple and Google.
When to use this skill
Trigger this skill when the user:
Wants to write or debug a Detox e2e test for a React Native app
Needs to set up Appium for native iOS or Android test automation
Asks about running tests on AWS Device Farm, Firebase Test Lab, or BrowserStack
Wants to configure crash reporting with Crashlytics, Sentry, or Bugsnag
Needs to distribute beta builds via TestFlight, Firebase App Distribution, or App Center
Asks about device matrix strategies or test sharding across real devices
Wants to symbolicate crash reports or set up dSYM/ProGuard mapping uploads
Is building a mobile CI/CD pipeline that includes automated testing and distribution
Do NOT trigger this skill for:
Web browser testing with Cypress, Playwright, or Selenium (those are web-specific)
React Native development questions unrelated to testing or distribution
Key principles
Test on real devices, not just simulators - Simulators miss touch latency, GPS
drift, camera behavior, memory pressure, and thermal throttling. Use simulators for
fast feedback during development, but gate releases on real-device test runs via
device farms.
Separate test layers by speed - Unit tests (Jest/XCTest) run in milliseconds
and cover logic. Integration tests verify module boundaries. E2e tests (Detox/Appium)
are slow and flaky by nature - reserve them for critical user journeys only (login,
purchase, onboarding). The pyramid still applies: many unit, fewer integration,
fewest e2e.
Treat crash reporting as a first-class signal - Ship no build without crash
reporting wired. Upload dSYMs and ProGuard mappings in CI, not manually. Monitor
crash-free rate as a release gate - below 99.5% should block rollout.
Automate beta distribution in CI - Never distribute builds manually. Every
merge to a release branch should trigger: build, test on device farm, upload to
beta channel, notify testers. Manual uploads break traceability and invite
version confusion.
Pin device matrices and OS versions - Define an explicit device/OS matrix in
your CI config. Test against the minimum supported OS, the latest OS, and 1-2
popular mid-range devices. Do not test against "all devices" - it is slow, expensive,
and the tail adds almost no signal.
Core concepts
Detox vs Appium - Detox is a gray-box testing framework built for React Native.
It synchronizes with the app's JS thread and native UI, eliminating most timing-related
flakiness. Appium is a black-box, cross-platform tool that uses the WebDriver protocol
to drive native apps, hybrid apps, or mobile web. Use Detox for React Native projects
(faster, less flaky). Use Appium when testing truly native apps (Swift/Kotlin) or when
you need cross-platform parity from a single test suite.
Device farms - Cloud services that maintain pools of real physical devices. You
upload your app binary and test suite, the farm runs tests across your chosen device
matrix, and returns results with logs, screenshots, and video. AWS Device Farm, Firebase
Test Lab, and BrowserStack App Automate are the major players. They differ in device
availability, pricing model, and integration depth with their respective ecosystems.
Crash reporting pipeline - The SDK (Crashlytics, Sentry, Bugsnag) captures uncaught
exceptions and native signals (SIGSEGV, SIGABRT) at runtime. Raw crash logs contain only
memory addresses. Symbolication maps these addresses back to source file names and line
numbers using debug symbols (dSYMs for iOS, ProGuard/R8 mapping files for Android).
Without symbolication, crash reports are unreadable.
Beta distribution - Getting pre-release builds to internal testers and external beta
users. Apple requires TestFlight for iOS (with mandatory App Store Connect processing).
Android is more flexible - Firebase App Distribution, direct APK/AAB sharing, or Play
Console internal tracks all work. Each channel has different compliance requirements,
device limits, and approval latencies.
Common tasks
Write a Detox e2e test for React Native
Detox tests use element matchers, actions, and expectations. The test synchronizes
automatically with animations and network calls.
Use simulators for dev speed, gate releases on device farm runs
Writing e2e tests for every screen
E2e tests are slow and flaky - a full suite takes 30+ min and breaks CI
Reserve e2e for 5-10 critical journeys; cover the rest with unit/integration
Skipping dSYM/ProGuard upload
Crash reports show raw memory addresses instead of file:line - unreadable
Automate symbol upload in CI as a mandatory post-build step
Manual beta distribution
Builds lose traceability, testers get wrong versions, QA is blocked
Automate distribution in CI triggered by branch/tag rules
Hardcoding device sleep/waits
sleep(5) is unreliable across device speeds and farm latency
Use Detox synchronization or Appium explicit waits with conditions
Testing against every OS version
Exponential matrix growth, diminishing returns past 3-4 versions
Pin min supported, latest, and 1-2 popular mid-range targets
Gotchas
Detox tests become flaky when testID props are missing on native components - Detox can only reliably target elements with testID set. Matching by text (by.text()) breaks as soon as a copy change or i18n update ships. Matching by type (by.type()) is fragile with component library upgrades. Add testID to every interactive element during development, not as a retroactive fix before testing.
TestFlight processing delay blocks release timelines - Apple processes uploaded builds for TestFlight before they are available to testers. This takes 15 minutes to 2+ hours. Teams that schedule beta distributions the day before a release window get caught waiting. Buffer at least 4 hours for TestFlight processing in your release plan, or upload the previous night.
dSYM upload failures are silent until a crash occurs - If the Crashlytics or Sentry dSYM upload step fails in CI (auth error, network timeout), the build succeeds but crash reports arrive unsymbolicated. You only discover this when the first crash report is unreadable. Add a post-build check that validates the dSYM was uploaded successfully, not just that the upload script exited 0.
Device farm tests run in a clean app state, which differs from upgrade paths - Device farms install the app fresh for every test run. They never test the upgrade path from a prior version, which is how 90%+ of your real users will encounter a new release. Run upgrade-path tests separately by pre-installing the current App Store version, then installing the new build over it, before running your test suite.
Appium session timeouts differ across farm providers - AWS Device Farm, Firebase Test Lab, and BrowserStack all have different default session timeout values (5-20 minutes). A test suite that runs fine locally or on one platform will time out silently on another. Set explicit newCommandTimeout capability values in your desired capabilities rather than relying on provider defaults.
References
For detailed content on specific topics, read the relevant file from references/:
references/detox-guide.md - Detox setup, configuration, matchers, actions, and CI integration
references/appium-guide.md - Appium server setup, desired capabilities, cross-platform patterns
references/device-farms.md - AWS Device Farm, Firebase Test Lab, BrowserStack comparison and setup
Only load a references file when the current task requires deep detail on that topic.
Companion check
On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:
