# Mutation Testing Baselines

> Sprint: SPRINT_0353_0001_0001_mutation_testing_integration
> Task: MUT-0353-005

This document tracks mutation testing baselines for critical modules.

## Baseline Scores

| Module | Initial Score | Target Score | Date Established |
|--------|--------------|--------------|------------------|
| Scanner.Core | 72% | ≥ 80% | 2025-12-16 |
| Policy.Engine | 68% | ≥ 80% | 2025-12-16 |
| Authority.Core | 75% | ≥ 85% | 2025-12-16 |
| Signer.Core | 70% | ≥ 80% | TBD |
| Attestor.Core | 65% | ≥ 80% | TBD |
| Reachability.Core | 60% | ≥ 75% | TBD |

## Threshold Configuration

See `stryker-thresholds.json` for per-module threshold configuration.

## Mutation Operators Applied

| Operator | Description | Enabled |
|----------|-------------|---------|
| Arithmetic | Replace +, -, *, /, % | ✓ |
| Boolean | Flip true/false | ✓ |
| Comparison | Replace <, >, <=, >=, ==, != | ✓ |
| Logical | Replace &&, ||, ! | ✓ |
| String | Mutate string literals | ✓ |
| Linq | Mutate LINQ methods | ✓ |
| NullCoalescing | Mutate ?? operators | ✓ |
| Assignment | Mutate assignment operators | ✓ |

## Exclusions

The following patterns are excluded from mutation testing:

- `**/Migrations/**` - Database migrations (tested via integration tests)
- `**/Generated/**` - Generated code
- `**/*.g.cs` - Source-generated files
- `**/Models/**` - Simple data transfer objects
- `**/Exceptions/**` - Exception types (tested via integration)

## Running Mutation Tests

### Local Execution

```bash
# Run mutation tests for a specific module
cd src/Scanner/__Libraries/StellaOps.Scanner.Core
dotnet stryker

# Run with specific configuration
dotnet stryker -f stryker-config.json --reporter html

# Quick mode (fewer mutations, faster feedback)
dotnet stryker --since:main
```

### CI Execution

Mutation tests run on:
- Merge requests targeting main
- Weekly scheduled runs (comprehensive)

Results are uploaded as artifacts and published to the mutation testing dashboard.

## Improving Mutation Score

1. **Add missing test cases** - Cover edge cases revealed by surviving mutants
2. **Strengthen assertions** - Replace weak assertions with specific ones
3. **Test boundary conditions** - Cover off-by-one and boundary scenarios
4. **Add negative tests** - Test that invalid inputs are rejected

## References

- [Stryker.NET Documentation](https://stryker-mutator.io/docs/stryker-net/)
- [Mutation Testing Guide](../testing/mutation-testing-guide.md)