Testing with Playwright MCP

CRITICAL: Always test changes before completion.

Subagent Delegation for Testing

Screenshot operations blow up context fast (~2000-5000 tokens each). Delegate to subagent for:

• Multi-step UI test scenarios
• Visual regression verification
• Accessibility audits
• Screenshot-heavy debugging

Delegation Pattern

runSubagent(
  prompt: "TESTING task with Playwright MCP.
    
    **Servers**: Frontend at localhost:5173, Backend at localhost:8080
    
    **Test Scenario**: [describe what to verify]
    
    **Steps**:
    1. Navigate to http://localhost:5173
    2. [specific actions to perform]
    
    **Check in priority order** (stop when answer found):
    1. Browser console logs - look for errors, state transitions (🔄)
    2. Network requests - verify API calls and status codes
    3. Accessibility snapshot - check element presence
    4. Screenshot - ONLY if visual verification essential
    
    **Return**:
    - Pass/Fail result
    - Specific evidence (error messages, status codes, element presence)
    - Console action log if relevant (🔄 ACTION_TYPE entries)
    
    Do NOT include raw screenshots or full accessibility dumps.",
  description: "Test: [what being verified]"
)

When to Delegate vs Inline

Testing Priority (Token efficiency)

1. Browser console logs – Check console messages for state transitions and errors
2. VS Code terminal logs – Check terminal output for backend/frontend server logs
3. Network requests – Inspect API calls and status codes
4. Accessibility snapshot – Get DOM structure for element verification
5. Screenshots – Visual verification (use sparingly, high token cost)

Key insight: Browser console shows React state changes (🔄 ACTION_TYPE), errors, and warnings. VS Code terminals show server logs and compilation output.

Workflow

Start servers in VS Code terminals (preferred – logs visible to AI agent):

# Run these VS Code tasks:
# - "Backend: ASP.NET Core API" (dotnet watch, port 8080)
# - "Frontend: React Vite" (npm run dev, port 5173)
# Or use compound task: "Start Dev (VS Code Terminals)"

Then test with Playwright MCP:

1. Navigate to http://localhost:5173
2. Check browser console for state transitions and errors
3. Verify network requests for API calls
4. Take accessibility snapshot for DOM validation

Check server logs:

• Check VS Code terminal output for backend compilation and request logs
• Backend terminal shows: request handling, errors, recompilation status
• Frontend terminal shows: HMR updates, build warnings, Vite output

When to Test

• After UI component or API endpoint changes
• Before committing multi-step implementations
• When user reports issues

Validation Checklist

• Console shows expected actions (🔄 [timestamp] ACTION_TYPE)
• No console errors/warnings
• Network tab shows correct status codes (200/400/401/500)
• DOM elements present in accessibility snapshot

State Logging (Dev Mode)

Each state change prints:

🔄 [HH:MM:SS] ACTION_TYPE
Action: { … }
Changes: { field: before → after }

Project-Specific: Key Test Scenarios

Project-Specific: Network Verification

Playwright MCP

Use console logs for state verification. Use snapshots for element presence. Avoid screenshots unless visual check required.

Related Skills

• validating-ui-features – Detailed test procedures for specific features
• writing-typescript-code – Frontend patterns and state management
• implementing-chat-streaming – SSE flow verification