/crap-analysis

name: crap-analysis
description: Analyze code coverage and CRAP (Change Risk Anti-Patterns) scores to identify high-risk code. Use OpenCover format with ReportGenerator for Risk Hotspots showing cyclomatic complexity and untested code paths.

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 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

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

Then restore:

dotnet tool restore

Or Install Globally

dotnet tool install --global dotnet-reportgenerator-globaltool

---

Collecting Coverage

Run Tests with Coverage Collection

# Clean previous results
rm -rf coverage/ TestResults/

# Run unit tests with coverage
dotnet test tests/MyApp.Tests.Unit \
  --settings coverage.runsettings \
  --collect:"XPlat Code Coverage" \
  --results-directory ./TestResults

# Run integration tests (optional, adds to coverage)
dotnet test tests/MyApp.Tests.Integration \
  --settings coverage.runsettings \
  --collect:"XPlat Code Coverage" \
  --results-directory ./TestResults

Generate HTML Report

dotnet reportgenerator \
  -reports:"TestResults/**/coverage.opencover.xml" \
  -targetdir:"coverage" \
  -reporttypes:"Html;TextSummary;MarkdownSummaryGithub"

Report Types

| Type | Description | Output | |------|-------------|--------| | `Html` | Full interactive report | `coverage/index.html` | | `TextSummary` | Plain text summary | `coverage/Summary.txt` | | `MarkdownSummaryGithub` | GitHub-compatible markdown | `coverage/SummaryGithub.md` | | `Badges` | SVG badges for README | `coverage/badge_*.svg` | | `Cobertura` | Merged Cobertura XML | `coverage/Cobertura.xml` |

---

Reading the Report

Risk Hotspots Section

The HTML report includes a **Risk Hotspots** section showing methods sorted by complexity:

• **Cyclomatic Complexity**: Number of independent paths through code (if/else, switch cases, loops)
• **NPath Complexity**: Number of acyclic execution paths (exponential growth with nesting)
• **Crap Score**: Calculated from complexity and coverage

Interpreting Results

Risk Hotspots
─────────────
Method                          Complexity  Coverage  Crap Score
─────