docs(platform): add TDD guidance to CLAUDE.md files (#12491)

Requested by @majdyz

Adds TDD (test-driven development) guidance to CLAUDE.md files so Claude
Code follows a test-first workflow when fixing bugs or adding features.

**Changes:**
- **Parent `CLAUDE.md`**: Cross-cutting TDD workflow — write a failing
`xfail` test, implement the fix, remove the marker
- **Backend `CLAUDE.md`**: Concrete pytest example with
`@pytest.mark.xfail` pattern
- **Frontend `CLAUDE.md`**: Note about using Playwright `.fixme`
annotation for bug-fix tests

The workflow is: write a failing test first → confirm it fails for the
right reason → implement → confirm it passes. This ensures every bug fix
is covered by a test that would have caught the regression.

---
Co-authored-by: Zamil Majdy (@majdyz) <zamil.majdy@agpt.co>

autogpt_platform/CLAUDE.md

@@ -68,6 +68,16 @@ AutoGPT Platform is a monorepo containing:
   ```
 - Run the github pre-commit hooks to ensure code quality.
 
+### Test-Driven Development (TDD)
+
+When fixing a bug or adding a feature, follow a test-first approach:
+
+1. **Write a failing test first** — create a test that reproduces the bug or validates the new behavior, marked with `@pytest.mark.xfail` (backend) or `.fixme` (Playwright). Run it to confirm it fails for the right reason.
+2. **Implement the fix/feature** — write the minimal code to make the test pass.
+3. **Remove the xfail marker** — once the test passes, remove the `xfail`/`.fixme` annotation and run the full test suite to confirm nothing else broke.
+
+This ensures every change is covered by a test and that the test actually validates the intended behavior.
+
 ### Reviewing/Revising Pull Requests
 
 Use `/pr-review` to review a PR or `/pr-address` to address comments.

autogpt_platform/backend/CLAUDE.md

@@ -85,6 +85,30 @@ poetry run pytest path/to/test.py --snapshot-update
 - After refactoring, update mock targets to match new module paths
 - Use `AsyncMock` for async functions (`from unittest.mock import AsyncMock`)
 
+### Test-Driven Development (TDD)
+
+When fixing a bug or adding a feature, write the test **before** the implementation:
+
+```python
+# 1. Write a failing test marked xfail
+@pytest.mark.xfail(reason="Bug #1234: widget crashes on empty input")
+def test_widget_handles_empty_input():
+    result = widget.process("")
+    assert result == Widget.EMPTY_RESULT
+
+# 2. Run it — confirm it fails (XFAIL)
+# poetry run pytest path/to/test.py::test_widget_handles_empty_input -xvs
+
+# 3. Implement the fix
+
+# 4. Remove xfail, run again — confirm it passes
+def test_widget_handles_empty_input():
+    result = widget.process("")
+    assert result == Widget.EMPTY_RESULT
+```
+
+This catches regressions and proves the fix actually works. **Every bug fix should include a test that would have caught it.**
+
 ## Database Schema
 
 Key models (defined in `schema.prisma`):

autogpt_platform/frontend/CLAUDE.md

@@ -84,7 +84,7 @@ See @CONTRIBUTING.md for complete patterns. Quick reference:
    - Regenerate with `pnpm generate:api`
    - Pattern: `use{Method}{Version}{OperationName}`
 4. **Styling**: Tailwind CSS only, use design tokens, Phosphor Icons only
-5. **Testing**: Add Storybook stories for new components, Playwright for E2E
+5. **Testing**: Add Storybook stories for new components, Playwright for E2E. When fixing a bug, write a failing Playwright test first (use `.fixme` annotation), implement the fix, then remove the annotation.
 6. **Code conventions**:
    - Use function declarations (not arrow functions) for components/handlers
    - Do not use `useCallback` or `useMemo` unless asked to optimise a given function