crap-analysis

Files (1)

• SKILL.md

SKILL.md (first lines)

# CRAP Score Analysis

## When to Use This Skill

Use this skill when:
- Evaluating code quality and test coverage before changes
- Identifying high-risk code that needs refactoring or testing
- Setting up coverage collection for a .NET project
- Prioritizing which code to test based on risk
- Establishing coverage thresholds for CI/CD pipelines

---

## What is CRAP?

**CRAP Score = Complexity x (1 - Coverage)^2**

The CRAP (Change Risk Anti-Patterns) score combines cyclomatic complexity with test coverage to identify risky code.

| CRAP Score | Risk Level | Action Required |
|------------|------------|-----------------|
| **< 5** | Low | Well-tested, maintainable code |
| **5-30** | Medium | Acceptable but watch complexity |
| **> 30** | High | Needs tests or refactoring |

### Why CRAP Matters

- **High complexity + low coverage = danger**: Code that's hard to understand AND untested is risky to modify
- **Complexity alone isn't enough**: A complex method with 100% coverage is safer than a simple method with 0%
- **Focuses effort**: Prioritize testing on complex code, not simple getters/setters

### CRAP Score Examples

| Method | Complexity | Coverage | Calculation | CRAP |
|--------|------------|----------|-------------|------|
| `GetUserId()` | 1 | 0% | 1 x (1 - 0)^2 | **1** |
| `ParseToken()` | 54 | 52% | 54 x (1 - 0.52)^2 | **12.4** |
| `ValidateForm()` | 20 | 0% | 20 x (1 - 0)^2 | **20** |
| `ProcessOrder()` | 45 | 20% | 45 x (1 - 0.20)^2 | **28.8** |
| `ImportData()` | 80 | 10% | 80 x (1 - 0.10)^2 | **64.8** |

---

## Coverage Collection Setup

### coverage.runsettings

Create a `coverage.runsettings` file in your repository root. The **OpenCover format is required** for CRAP score calculation because it includes cyclomatic complexity metrics.

```xml
<?xml version="1.0" encoding="utf-8" ?>
<RunSettings>
  <DataCollectionRunSettings>
    <DataCollectors>
      <DataCollector friendlyName="XPlat code coverage">
        <Configuration>
          <!-- OpenCover format includes cyclomatic complexity for CRAP scores -->
          <Format>cobertura,opencover</Format>

          <!-- Exclude test and benchmark assemblies -->
          <Exclude>[*.Tests]*,[*.Benchmark]*,[*.Migrations]*</Exclude>

          <!-- Exclude generated code, obsolete members, and explicit exclusions -->
          <ExcludeByAttribute>Obsolete,GeneratedCodeAttribute,CompilerGeneratedAttribute,ExcludeFromCodeCoverageAttribute</ExcludeByAttribute>

          <!-- Exclude source-generated files, Blazor generated code, and migrations -->
          <ExcludeByFile>**/obj/**/*,**/*.g.cs,**/*.designer.cs,**/*.razor.g.cs,**/*.razor.css.g.cs,**/Migrations/**/*</ExcludeByFile>

          <!-- Exclude test projects -->
          <IncludeTestAssembly>false</IncludeTestAssembly>

          <!-- Optimization flags -->
          <SingleHit>false</SingleHit>
          <UseSourceLink>true</UseSourceLink>
          <SkipAutoProps>true</SkipAutoProps>
        </Configuration>
      </DataCollector>
    </DataCollectors>
  </DataCollectionRunSettings>
</RunSettings>
```

### Key Configuration Options

| Option | Purpose |
|--------|---------|
| `Format` | Must include `opencover` for complexity metrics |
| `Exclude` | Exclude test/benchmark assemblies by pattern |
| `ExcludeByAttribute` | Skip generated, obsolete, and explicitly excluded code (includes `ExcludeFromCodeCoverageAttribute`) |
| `ExcludeByFile` | Skip source-generated files, Blazor components, and migrations |
| `SkipAutoProps` | Don't count auto-properties as branches |

---

## ReportGenerator Installation

Install ReportGenerator as a local tool for generating HTML reports with Risk Hotspots.

### Add to .config/dotnet-tools.json

```json
{
  "version": 1,
  "isRoot": true,
  "tools": {
    "dotnet-reportgenerator-globaltool": {
      "version": "5.4.5",
      "commands": ["reportgenerator"],
      "rollForward": false
    }
  }
}
```

Then restore:

```bash
dotnet tool restore
```

From ComeOnOliver/skillshub, MIT.

More from ComeOnOliver/skillshub