Mobile E2E Testing via MCP

Verified workflow for running functional (not render-only) tests on Expo/React Native apps using mcporter CLI + claude-in-mobile MCP server. Derived from a real debugging session on biolift/JSTLFT — 24/24 functional tests passed against real production Firebase on Android emulator.

When to use

• User wants functional validation of a mobile app (set logging, form submission, navigation + state persistence, etc.)
• Expo Go SDK 54+ or a custom dev build
• App uses Firebase (Auth + Firestore) or a similar cloud backend
• Target: Android emulator (strongly preferred) or iOS simulator (requires WDA setup — see Gotchas)

Prerequisites

• mcporter CLI installed globally: npm install -g mcporter
• claude-in-mobile MCP server registered in ~/.mcporter/mcporter.json:

  {
    "mcpServers": {
      "mobile": {
        "command": "npx",
        "args": ["-y", "claude-in-mobile@latest"],
        "description": "Native app testing via simulator/emulator (iOS + Android)"
      }
    }
  }
  

• Android SDK with at least one AVD created (e.g. Medium_Phone_API_35)
• ADB in PATH or at ~/Library/Android/sdk/platform-tools/adb
• Real credentials for the app's backend (or Firebase emulator, or a mock-auth code path)

Android workflow (recommended)

1. Boot emulator in tmux

tmux new-session -d -s emu
tmux send-keys -t emu "~/Library/Android/sdk/emulator/emulator -avd <avd-name> -no-snapshot-save -no-boot-anim" C-m
~/Library/Android/sdk/platform-tools/adb wait-for-device
~/Library/Android/sdk/platform-tools/adb shell 'while [[ -z $(getprop sys.boot_completed) ]]; do sleep 1; done; echo boot-completed'

2. Configure app to use real backend

Grep the repo for production config files: find . -name "*-config.json" -not -path "*/node_modules/*". Common names: firebase-applet-config.json, credentials.json, google-services.json. Copy credentials into mobile/.env.local (gitignored). Don't waste time with dummy Firebase keys — they get rejected with auth/api-key-not-valid at the Auth layer.

3. Start Metro in tmux

tmux new-session -d -s metro -c /path/to/mobile
tmux send-keys -t metro "EXPO_NO_TELEMETRY=1 npx expo start --android --clear" C-m
# Expo shows interactive auth prompt — answer it programmatically:
sleep 15
tmux send-keys -t metro Down C-m  # selects "Proceed anonymously"

4. Port forward (critical)

~/Library/Android/sdk/platform-tools/adb reverse tcp:8081 tcp:8081

Without this the emulator can't reach Metro and Expo Go shows "Something went wrong / Failed to download remote update".

5. Set mcporter target device

mcporter call mobile.device_set --args '{"deviceId": "emulator-5554", "platform": "android"}'

6. Dismiss first-launch dev menu

On first launch, Expo Go shows a bottom sheet with "Continue" and an X. Tap the X at top-right (approx 966, 1740), not Continue — Continue advances to the Tools page instead of dismissing.

7. Screenshot + tap loop

# Screenshot (always decode base64 via python)
mcporter call mobile.screen_capture --args '{"platform": "android"}' --output json > /tmp/mcp.json
python3 -c "
import json, base64
with open('/tmp/mcp.json') as f: d = json.load(f)
for item in d.get('content', []):
    if item.get('type') == 'image':
        with open('/tmp/shot.jpg', 'wb') as f: f.write(base64.b64decode(item['data']))
"

# Find elements precisely (never guess coordinates)
mcporter call mobile.ui_find --args '{"platform": "android", "text": "Get Started", "clickable": true}'
# Returns: [27] <ViewGroup> desc="Get Started" (clickable) @ (540, 1620)

# Tap at returned coordinates
mcporter call mobile.input_tap --args '{"platform": "android", "x": 540, "y": 1620}'

# Type into focused field
mcporter call mobile.input_text --args '{"platform": "android", "text": "chicken"}'

Screen coordinate reference

• Original resolution on Medium_Phone_API_35: 1080×2400 — use these in input_tap
• Screenshot preview display: 540×1200 (×2 scale factor)
• Bottom tab bar y ≈ 2310
• For N tabs across 1080 width: tab N center at x = (1080/N)/2 + index*(1080/N)

Three ways to unblock Firebase auth

1. Production credentials (fastest if available):

   • Grep repo for *-config.json
   • Copy to mobile/.env.local
   • Works for real auth + real Firestore

2. Firebase emulator:

   • firebase emulators:start --only auth,firestore --project <dummy-project>
   • Requires JDK 21+ (firebase-tools 15+)
   • Requires connectAuthEmulator / connectFirestoreEmulator wiring in the app
   • Android emulator uses 10.0.2.2 as host loopback alias (not localhost)
   • Set env flag like FIREBASE_USE_EMULATOR=true to gate the wiring

3. Mock auth bypass:

   • Add an EXPO_PUBLIC_DEV_MOCK_AUTH env var check in your Auth provider
   • Skip real sign-in, inject a fake User object, pretend onboarding completed
   • Fastest iteration but limited to UI-only testing (Firestore calls will still fail)

Pick the first one that applies — production creds are almost always the simplest.

Common Gotchas

Symptom	Cause	Fix
auth/api-key-not-valid	Dummy Firebase config in .env.local	Copy real creds from repo config file
"Failed to download remote update"	No adb reverse	adb reverse tcp:8081 tcp:8081 after both emulator + Metro are up
Metro halts at "Log in / Proceed anonymously"	Interactive prompt blocks auto-execution	tmux send-keys <session> Down C-m selects anonymous
Tap does nothing visible	Expo dev menu overlay absorbing taps	Tap the X at top-right, NOT "Continue"
Inspector mode activated accidentally	Tapped "Toggle element inspector" in Tools page	Reload app (send r to Metro tmux)
VirtualView*NativeComponent red screen	RN version mismatch with Expo SDK	npx expo install --fix to realign dep matrix
Cannot find native module 'ExponentAV'	expo-av removed in SDK 54+	Migrate to expo-audio (createAudioPlayer, setAudioModeAsync)
expo-notifications: Android Push notifications removed	SDK 53+ removed expo-notifications from Android Expo Go	Create platform-split shim: notificationsShim.android.ts (noop stubs) + notificationsShim.ios.ts (re-export) + default notificationsShim.ts
MCP tools not available in Claude Code session	Added mid-session, schemas not loaded	Use mcporter call from shell — bypasses schema requirement
iOS tap returns "WDA not found"	WebDriverAgent not compiled + installed	Switch to Android. Don't go down the WDA rabbit hole unless iOS-specific testing is mandatory
mcporter config add --scope home mobile fails	Flag parser treats --scope as positional name	Edit ~/.mcporter/mcporter.json directly instead

Firestore integration smoke test

A great indicator that the full stack is working: the cross-tab integration test.

1. Complete a workout in the Workout tab (log sets → finish)
2. Navigate to Progress tab
3. Assert the PR count incremented by the number of new PRs you set

If this works, Firestore reads/writes are healthy and the app's realtime subscriptions are wired correctly.

Anti-patterns to avoid

• Guessing tap coordinates from screenshots. Use ui_find every time. Coordinates drift between devices, orientations, and theme changes.
• Declaring "tested" on render. A screen can render perfectly and still have broken onClick handlers. Always tap through.
• Starting Metro before the emulator is ready. Metro crashes with adb shell pm list packages ... exited with non-zero code: 1. Wait for boot_completed first.
• Reloading via Expo CLI r during an auth prompt session. Each reload re-triggers the auth prompt. Do all reloads after the prompt is already answered.
• Trying iOS first. WDA setup burns hours. Default to Android.

Evidence

This skill was derived from a real 2-hour debugging session testing the biolift (JSTLFT) mobile app on Android via mcporter. 24 functional tests passed end-to-end against real production Firebase, including:

• Firebase Anonymous Auth (real production sign-in)
• Onboarding wizard (sport → position → program)
• Live workout execution with inline PR detection + rest timer
• Nutrition meal logging with macro ring updates
• Theme switch with AsyncStorage cross-screen persistence
• Cross-tab PR count verification

Full test log: search the project for research/*functional-test-results.md.