chore: import upstream snapshot with attribution

.github/instructions/testing.instructions.md

@@ -0,0 +1,98 @@
+---
+applyTo: "**/*.{ts,tsx,js,jsx}"
+---
+
+# Test Coverage Review Instructions
+
+Review code changes for adequate test coverage using freeCodeCamp's testing conventions.
+
+## Testing Framework Reference
+
+| Location | Framework | File Pattern | Notes |
+|----------|-----------|--------------|-------|
+| `api/` | Vitest | `*.test.ts` | Co-located with source |
+| `client/` | Vitest | `*.test.{ts,tsx}` | Co-located with source |
+| `e2e/` | Playwright | `*.spec.ts` | Dedicated directory |
+
+## When to Flag Missing Tests
+
+Comment on missing tests if ALL of these are true:
+
+- PR modifies functional code (bug fix or new feature)
+- No corresponding test additions or modifications exist
+- Changes are not test-only or config-only
+
+### Examples Requiring Tests
+
+- New utility functions in `api/src/utils/` or `client/src/utils/`
+- New API route handlers in `api/src/routes/`
+- New React components with logic in `client/src/components/`
+- Bug fixes that change application behavior
+- New validation logic or data transformations
+
+## When NOT to Flag
+
+Do not comment on test coverage if:
+
+- Changes are documentation, configuration, or non-functional
+- PR already includes appropriate test coverage
+- Changes are to test files themselves
+- Changes are trivial:
+  - Import reorganization
+  - Formatting changes
+  - Type-only changes (interfaces, type definitions)
+  - Comment updates
+- Changes are in areas without existing test patterns:
+  - Curriculum markdown files
+  - Configuration files
+  - Build scripts
+
+## Detecting Outdated Tests
+
+Flag if existing tests may be outdated:
+
+- Test file exists for modified source but doesn't cover the changed functionality
+- Test assertions reference behavior that is being changed
+- Mock data doesn't reflect new data structures or API responses
+- Test descriptions no longer match actual test behavior
+
+### Example Comment for Outdated Tests
+
+```
+Tests in `src/utils/validate.test.ts` need updates for new validation rules.
+```
+
+## Comment Format
+
+### Missing Tests
+
+Brief, actionable feedback only:
+
+```
+Missing tests for `src/utils/validate.ts`:
+- Valid input case
+- Invalid input error
+- Empty string edge case
+```
+
+### Sufficient Coverage
+
+**DO NOT COMMENT.** Silence means approval.
+
+### Outdated Tests
+
+```
+Tests in `[test file]` need updates for `[source file]` changes:
+- [specific change]
+```
+
+## Test Quality Indicators
+
+When tests are present, briefly verify:
+
+- Tests cover the happy path
+- Tests cover at least one error/edge case
+- Test descriptions are meaningful (not just "test 1", "test 2")
+- Mocks are appropriate (not mocking the thing being tested)
+
+Do not block PRs for test style preferences if coverage is adequate.