Mobile webview testing

Mobile WebView Testing

Test any Capacitor, Ionic, or WebView hybrid app on a real Android device.

The core insight: uiautomator cannot see WebView content. Your entire app UI is invisible to native Android automation tools. This skill uses Chrome DevTools Protocol (CDP) for web elements and uiautomator only for native system dialogs — a hybrid approach that covers 100% of the UI.

Prerequisites

• Android device connected via USB with USB debugging enabled
• adb available in PATH
• Python 3 with websockets package (pip3 install websockets)

Phase 1: Connect to WebView via CDP

Every WebView-based app exposes a DevTools socket. Connect to it in 4 steps:

Step 1: Get the app's PID

PID=$(adb shell pidof com.example.myapp)
echo "PID: $PID"

Step 2: Forward the DevTools port

adb forward tcp:9222 localabstract:webview_devtools_remote_${PID}

Step 3: Get the WebSocket debug URL

curl -s http://localhost:9222/json | python3 -c \
  "import sys,json; pages=json.load(sys.stdin); print(pages[0]['webSocketDebuggerUrl'])"

Step 4: Connect via Python

import json, asyncio, websockets

async def cdp_eval(ws_url, js_expression):
    async with websockets.connect(ws_url) as ws:
        cmd = {
            "id": 1,
            "method": "Runtime.evaluate",
            "params": {"expression": js_expression, "returnByValue": True}
        }
        await ws.send(json.dumps(cmd))
        resp = json.loads(await ws.recv())
        return resp.get("result", {}).get("result", {}).get("value", "")

Or use the bundled helper: scripts/cdp-connect.sh <package.name> prints the WebSocket URL.

Phase 2: Execute JavaScript in WebView

IIFE Isolation (Critical)

CDP's Runtime.evaluate shares a single global scope across all calls in the same session. Declaring a variable twice causes SyntaxError: Identifier has already been declared.

Always wrap code in an IIFE:

(function() {
    const result = document.querySelector('.my-element');
    return result ? result.textContent : 'not found';
})()

Query DOM Elements

// List all buttons
(function() {
    return JSON.stringify(
        Array.from(document.querySelectorAll('button')).map((b, i) => ({
            i,
            text: b.textContent?.trim().substring(0, 60),
            cls: b.className
        }))
    );
})()

Click Elements

// Click by CSS selector
document.querySelector('.submit-btn').click()

// Click by index (useful when selectors are unreliable)
document.querySelectorAll('button')[2].click()

Navigate

// SPA hash navigation
window.location.hash = '#settings';

// Full navigation
window.location.href = '/dashboard';

Phase 3: Interact with Framework State

React (Most Common for Capacitor/Ionic)

Standard DOM .value = x does NOT trigger React state updates. React uses synthetic events and ignores direct property changes on controlled inputs.

Solution: Use React's internal __reactProps key:

(function() {
    const input = document.querySelector('input.my-input');
    const propsKey = Object.keys(input).find(k => k.startsWith('__reactProps'));
    const props = input[propsKey];
    input.value = 'Hello from CDP';
    props.onChange({ target: input });
    return input.value;
})()

This works for <input>, <textarea>, and <select> elements.

For <select> elements:

(function() {
    const select = document.querySelector('select.language-picker');
    const propsKey = Object.keys(select).find(k => k.startsWith('__reactProps'));
    const props = select[propsKey];
    props.onChange({ target: { value: 'fr' } });
    return 'switched';
})()

See REACT-STATE.md for advanced patterns (checkboxes, radio buttons, custom components).

Vue / Angular

See FRAMEWORK-SUPPORT.md for Vue's __vue__ and Angular's ng.getComponent approaches.

Phase 4: Handle Native UI Elements

System dialogs (permission prompts, file pickers, share sheets) are native Android UI, not WebView content. Use uiautomator for these:

Dump the UI hierarchy

adb shell uiautomator dump /data/local/tmp/ui.xml
adb pull /data/local/tmp/ui.xml /tmp/ui.xml

Parse clickable elements

import xml.etree.ElementTree as ET

tree = ET.parse('/tmp/ui.xml')
for node in tree.iter('node'):
    text = node.get('text', '')
    bounds = node.get('bounds', '')
    clickable = node.get('clickable', '')
    if text and clickable == 'true':
        print(f'{bounds} | text={text}')

Tap by coordinates

Parse [x1,y1][x2,y2] bounds and tap the center:

# Example: bounds [540,1200][900,1300] → center (720, 1250)
adb shell input tap 720 1250

The Hybrid Strategy

Element Type	Tool	Example
Web buttons, inputs, text	CDP Runtime.evaluate	App UI, forms, navigation
Permission dialogs	uiautomator + input tap	"Allow camera access"
File/photo picker	uiautomator + input tap	Gallery selection
System notifications	uiautomator dump	Toast messages

Or use the bundled helper: scripts/native-ui-parser.py automates XML parsing.

Phase 5: Screenshots & Visual Verification

Capture a screenshot

adb exec-out screencap -p > /tmp/screenshot.png

Verify with AI vision

If your AI assistant supports image input, read the screenshot file to visually verify the UI state. This is especially useful for:

• Layout verification after language switching (e.g., RTL Arabic)
• Visual regression detection
• Confirming modal dialogs appeared correctly
• Verifying responsive design on different screen sizes

Phase 6: Network Testing

Disable network (test offline mode)

adb shell svc wifi disable
adb shell svc data disable

Re-enable network

adb shell svc wifi enable
adb shell svc data enable

Note: Settings.Global.AIRPLANE_MODE broadcast requires system privileges and will fail on most non-rooted devices. Use svc wifi/data instead.

Test flow

1. Ensure app works normally with network
2. Disable wifi + data
3. Perform core actions (verify offline functionality)
4. Re-enable network
5. Verify data syncs correctly

Phase 7: Debugging

Filter logcat

# Clear previous logs
adb logcat -c

# Perform the action you want to debug...

# Capture filtered logs
adb logcat -d | grep -iE "error|exception|crash|your-app-tag" | tail -30

Capture WebView console logs via CDP

# Enable Console domain
await ws.send(json.dumps({"id": 2, "method": "Console.enable"}))

# Listen for console messages
while True:
    msg = json.loads(await ws.recv())
    if msg.get("method") == "Console.messageAdded":
        entry = msg["params"]["message"]
        print(f"[{entry['level']}] {entry['text']}")

Monitor network requests via CDP

# Enable Network domain
await ws.send(json.dumps({"id": 3, "method": "Network.enable"}))

# Listen for responses
while True:
    msg = json.loads(await ws.recv())
    if msg.get("method") == "Network.responseReceived":
        resp = msg["params"]["response"]
        print(f"{resp['status']} {resp['url']}")

Phase 8: Advanced Techniques

Push large files to app internal storage

Apps cannot read from /sdcard/ in scoped storage. Use run-as to write to the app's private directory:

# Push to temp location
adb push ./large-file.bin /data/local/tmp/

# Move into app's internal storage
adb shell run-as com.example.myapp mkdir -p files/data
adb shell "cat /data/local/tmp/large-file.bin | \
  run-as com.example.myapp sh -c 'cat > files/data/large-file.bin'"

Handle CDP reconnection after app restart

After am force-stop, the WebSocket URL changes. Full reconnection flow:

# Restart the app
adb shell am force-stop com.example.myapp
adb shell am start -n com.example.myapp/.MainActivity

# Wait for WebView to initialize
sleep 3

# Re-discover PID and reconnect
PID=$(adb shell pidof com.example.myapp)
adb forward tcp:9222 localabstract:webview_devtools_remote_${PID}
# Fetch new WebSocket URL from /json endpoint

Handle multiple WebView pages

Some apps have multiple WebView pages (e.g., main app + in-app browser):

# List all debuggable pages
curl -s http://localhost:9222/json
# Returns an array — pick the page by title or URL

import json, urllib.request

pages = json.loads(urllib.request.urlopen("http://localhost:9222/json").read())
for p in pages:
    print(f"  {p['title']} → {p['webSocketDebuggerUrl']}")

Common Pitfalls

See COMMON-PITFALLS.md for 8 battle-tested pitfalls and their solutions, learned from real production testing.

Test Checklist

See TEST-CHECKLIST.md for a reusable 12-point test template covering app launch, input interaction, navigation, offline mode, and more.