# QUALITY-008: Coverage Regression Prevention

## Summary
Establish automated systems to prevent test coverage regressions and maintain the quality baseline achieved during the coverage sprint.

## Background
Coverage sprint achieved 37.13% overall coverage with significant improvements in transpiler (54.85%) and interpreter (69.57%). Need to prevent backsliding and ensure sustainable quality improvements.

## Scope

### Pre-commit Hooks Enhancement
- Integrate coverage checking into existing quality gates
- Set minimum coverage thresholds (current baseline)
- Block commits that decrease coverage
- Provide actionable feedback on coverage changes

### GitHub Actions Integration
- Automated coverage reporting on PRs
- Coverage trend visualization
- Regression alerts and notifications
- Integration with existing CI/CD pipeline

### Documentation and Training
- Update CLAUDE.md with coverage requirements
- Create developer guides for maintaining coverage
- Document coverage analysis workflow
- Establish team practices and standards

## Implementation Plan

### Phase 1: Enhanced Pre-commit Hooks (3-5 days)
```bash
# Add to .git/hooks/pre-commit
echo "🔍 Coverage regression check..."
CURRENT_COVERAGE=$(cargo llvm-cov report --ignore-filename-regex "tests/" | grep "TOTAL" | awk '{print $4}' | sed 's/%//')
BASELINE_COVERAGE=37.13

if (( $(echo "$CURRENT_COVERAGE < $BASELINE_COVERAGE" | bc -l) )); then
    echo "❌ BLOCKED: Coverage decreased from $BASELINE_COVERAGE% to $CURRENT_COVERAGE%"
    echo "💡 Add tests to maintain coverage baseline"
    exit 1
fi
```

### Phase 2: GitHub Actions Coverage (2-3 days)
- Create coverage workflow for PRs
- Generate coverage reports and diffs
- Comment on PRs with coverage changes
- Store coverage history and trends

### Phase 3: Documentation Updates (1-2 days)
- Update quality requirements in CLAUDE.md
- Create coverage maintenance guides
- Document tooling and workflows
- Establish team standards

## Success Criteria

### Automated Prevention
- [ ] Pre-commit hooks block coverage decreases
- [ ] GitHub Actions report coverage on all PRs
- [ ] Regression alerts sent to team
- [ ] Coverage trends tracked over time

### Team Adoption
- [ ] Documentation updated and accessible
- [ ] Developer workflow integrated seamlessly
- [ ] Clear guidelines for maintaining coverage
- [ ] Training materials available

### Sustainability Metrics
- **Coverage Baseline**: Maintain 37.13% minimum
- **Transpiler Baseline**: Maintain 54.85% minimum  
- **Interpreter Baseline**: Maintain 69.57% minimum
- **Regression Rate**: <2% acceptable temporary decreases

## Technical Requirements

### Coverage Baselines
```yaml
baselines:
  overall: 37.13%
  transpiler: 54.85%
  interpreter: 69.57%
  repl: 8.33%
  
thresholds:
  warning: -1.0%    # Yellow flag
  blocking: -2.0%   # Red flag, block merge
  critical: -5.0%   # Escalate to team lead
```

### Tooling Integration
- Leverage existing `scripts/coverage.sh`
- Integrate with current quality gates
- Use existing `cargo llvm-cov` infrastructure
- Minimal additional dependencies

### Performance Constraints
- Coverage check must complete in <30 seconds
- No significant impact on development workflow
- Fail fast with clear error messages
- Option to override in emergency situations

## Dependencies
- **Requires**: Coverage infrastructure (QUALITY-001 to QUALITY-006 - completed)
- **Blocks**: Advanced testing initiatives (QUALITY-009+)
- **Integrates with**: Existing pre-commit hooks and CI/CD

## Risk Mitigation

### False Positives
- Allow temporary coverage decreases with justification
- Override mechanism for emergency fixes
- Regular baseline updates for intentional changes
- Clear documentation of exceptions

### Developer Experience
- Fast feedback loops (<30 seconds)
- Clear, actionable error messages
- Easy local reproduction of issues
- Minimal workflow disruption

### Maintenance Burden
- Leverage existing tooling where possible
- Automated baseline updates
- Self-documenting configuration
- Minimal manual intervention required

## Acceptance Criteria

### Functional Requirements
- [ ] Pre-commit hooks integrated with coverage checking
- [ ] GitHub Actions workflow for PR coverage reporting
- [ ] Documentation updated with coverage requirements
- [ ] Team training materials created

### Quality Gates
- [ ] Coverage regressions are automatically detected
- [ ] Clear feedback provided to developers
- [ ] Override mechanisms work correctly
- [ ] No false positives in normal workflow

### Performance Requirements
- [ ] Coverage check completes in <30 seconds
- [ ] No significant impact on commit/push times
- [ ] CI/CD pipeline integration seamless
- [ ] Local development workflow unaffected

## Definition of Done
- Pre-commit hooks enhanced with coverage checking
- GitHub Actions workflow deployed and tested
- Documentation updated and reviewed
- Team onboarded to new processes
- Monitoring and alerting configured
- Sprint retrospective completed with lessons learned