Official agent skill

Coverage Analysis

by microsoft in microsoft/testfx

Project-wide code coverage and CRAP (Change Risk Anti-Patterns) score analysis for .NET projects.

OfficialMITAuto-check passedTesting & QA

Install Coverage Analysis

skills CLI
$ npx skills add microsoft/testfx --skill coverage-analysis -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install microsoft/testfx coverage-analysis --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/microsoft/testfx.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/coverage-analysis .claude/skills/coverage-analysis && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
coverage-analysis
GitHub stars
1k
Token cost
~7.3k tokens
SKILL.md length
2,101 words
Files
5 (incl. scripts, references)
Skills in repo
44
Repo updated
First seen
Licence
MIT

At a glance

Project-wide code coverage and CRAP (Change Risk Anti-Patterns) score analysis for .NET projects.

  • Works in 5 steps: Setup (sequential) → Test execution (skip when Cobertura XML… → Analysis (sequential) → …
  • Diagnose why coverage is stuck
  • SKILL.md covers Purpose, When to Use, When Not to Use and Inputs, plus 3 more sections
  • Runs PowerShell scripts from its folder; calls dotnet

What it does

Coverage Analysis is an agent skill from microsoft/testfx, published by the product's own GitHub organization. Project-wide code coverage and CRAP (Change Risk Anti-Patterns) score analysis for .NET projects. Calculates CRAP scores per method and surfaces risk hotspots — complex code with low coverage that is dangerous to modify. Use to diagnose why coverage is stuck or plateaued, identify what methods block improvement, or get project-wide coverage analysis with risk ranking. USE FOR: coverage stuck, coverage plateau, can't increase coverage, what's blocking coverage, coverage gap, CRAP scores, risk hotspots, where to…

Its SKILL.md is about 7.3k tokens, which your agent loads only when the skill is triggered. The skill folder holds 6 other files, including scripts and reference files (for example `references/guidelines.md` and `references/output-format.md`).

It sits in Testing & QA, covering Test coverage. It works with .NET. The repository describes itself as: This repository holds the source code of Microsoft.Testing.Platform (MTP), a lightweight alternative to VSTest, as well as MSTest adapter and framework. The licence is MIT.

When your agent uses it

  • Diagnose why coverage is stuck
  • Identify what methods block improvement
  • Get project-wide coverage analysis with risk ranking
  • : coverage stuck

Example prompts

  • “t increase coverage, what”
  • “/coverage-analysis”

Requirements

  • PowerShell

Workflow steps

5 steps, taken from the step headings in SKILL.md.

  1. Setup (sequential)
  2. Test execution (skip when Cobertura XML already exists)
  3. Analysis (sequential)
  4. User-facing summary (MANDATORY — your next assistant response)
  5. Optional: ReportGenerator HTML/CSV reports (post-summary)

What it can do on your machine

Read from SKILL.md and the folder at commit 44b9dcc. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Ships 2 files in scripts/ (PowerShell), which the agent can run.

    Shell commands in SKILL.md call:

    • dotnet

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Coverage Analysis loads about 7.3k tokens when it runs, and up to ~9.5k if it reads all its reference files. Until then it costs about 187 tokens; SKILL.md has 2,101 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~187
When it runs · the whole SKILL.md, loaded when a task matches
~7.3k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~9.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.

SKILL.md

The full file from microsoft/testfx at commit 44b9dcc, republished under its MIT licence (© microsoft). 2,101 words, ~7,250 tokens.

Download SKILL.mdSave it as .claude/skills/coverage-analysis/SKILL.md (or your agent's skills folder). This skill also uses 4 other files; get the full folder from GitHub.
name
coverage-analysis
description
Project-wide code coverage and CRAP (Change Risk Anti-Patterns) score analysis for .NET projects. Calculates CRAP scores per method and surfaces risk hotspots — complex code with low coverage that is dangerous to modify. Use to diagnose why coverage is stuck or plateaued, identify what methods block improvement, or get project-wide coverage analysis with risk ranking. USE FOR: coverage stuck, coverage plateau, can't increase coverage, what's blocking coverage, coverage gap, CRAP scores, risk hotspots, where to add tests, coverage analysis, coverage report. DO NOT USE FOR: targeted single-method CRAP analysis (use crap-score), writing tests, running tests without coverage, or troubleshooting test execution (use run-tests).
license
MIT

Coverage Analysis

Purpose

Raw coverage percentages answer "what code was executed?" — they don't answer what you actually need to know:

  • What tests should I write next? — ranked by risk and impact
  • Which uncovered code is risky vs. trivial? — CRAP scores separate the two
  • Why has coverage plateaued? — identify the files blocking further gains
  • Is this code safe to refactor? — complex + uncovered = dangerous to change

This skill bridges that gap: from a bare .NET solution to a prioritized risk hotspot list, with no manual tool configuration required.

When to Use

Use this skill when the user mentions test coverage, coverage gaps, code risk, CRAP scores, where to add tests, why coverage plateaued, or wants to know which code is safest to refactor — even if they don't explicitly say "coverage analysis".

When Not to Use

  • Targeted single-method CRAP analysis — use the crap-score skill instead
  • Writing or generating tests — this skill identifies where tests are needed, not write them
  • General test execution unrelated to coverage or CRAP analysis
  • Coverage reporting without CRAP context — use dotnet test with coverage collection directly

Inputs

InputRequiredDefaultDescription
Project/solution pathNoCurrent directoryPath to the .NET solution or project
Line coverage thresholdNo80%Minimum acceptable line coverage
Branch coverage thresholdNo70%Minimum acceptable branch coverage
CRAP thresholdNo30Maximum acceptable CRAP score before flagging
Top N hotspotsNo10Number of risk hotspots to surface
Prerequisites
  • .NET SDK installed (dotnet on PATH)
  • At least one test project referencing the production code (xUnit, NUnit, or MSTest) — only required for the from-scratch path; not needed when the user supplies an existing Cobertura XML
  • Optional, only for the from-scratch path: internet/NuGet access for dotnet add package coverlet.collector (or Microsoft.Testing.Extensions.CodeCoverage) when a test project has no coverage provider yet. Skip when the user supplies an existing Cobertura XML.
  • Optional, only for Phase 5: internet access for dotnet tool install (ReportGenerator). Core CRAP/coverage analysis works from Cobertura XML alone — ReportGenerator only adds HTML/CSV reports as an optional post-summary extra.

The skill auto-detects coverage provider state per test project and selects the least-invasive execution strategy:

  • unified Microsoft CodeCoverage when all projects use it,
  • unified Coverlet when no project uses Microsoft CodeCoverage,
  • per-project provider execution when the solution is truly mixed.

No pre-existing runsettings files or manually installed tools required.

Workflow

MANDATORY: deliver the final assistant response with the CRAP/risk-hotspot summary BEFORE any optional work. As soon as Compute-CrapScores.ps1 and Extract-MethodCoverage.ps1 return data, your next assistant response must contain the user-facing analysis (CRAP table, blocking methods, recommendations). Do not run ReportGenerator (Phase 5), do not install global tools, and do not start any heavy parallel work before that response is delivered. The user is judged on the final assistant message, not on side-effect files.

If a phase fails, times out, or budget is running low, skip remaining optional work and immediately return a partial summary containing: (1) what was found in the Cobertura XML, (2) any CRAP/risk-hotspot data already extracted, (3) which methods are blocking coverage, and (4) failures encountered.

If the user provides a path to existing Cobertura XML (or coverage data is already present in TestResults/), skip Phase 2 entirely (no test execution) and skip Phase 5 by default (no ReportGenerator install or HTML report) — go directly from Phase 3 (analysis scripts) to Phase 4 (user-facing summary). Only run Phase 5 if the user explicitly asks for HTML/CSV reports. The Risk Hotspots table and CRAP scores are mandatory in every output — they are the skill's core value-add over raw coverage numbers.

The workflow runs in five phases. Phases 1–4 are required; Phase 5 (ReportGenerator HTML/CSV reports) is strictly optional and runs after the user-facing summary has been delivered. Do not parallelize Phase 5 with earlier phases — the heavy dotnet tool install for ReportGenerator can crash the session before Phase 4 completes.

Phase 1 — Setup (sequential)
Step 1: Locate the solution or project

Given the user's path (default: current directory), find the entry point:

powershell
$root = "<user-provided-path-or-current-directory>"

# Prefer solution file; fall back to project file
$sln = Get-ChildItem -Path $root -Filter "*.sln" -Recurse -Depth 2 -ErrorAction SilentlyContinue |
    Select-Object -First 1
if ($sln) {
    Write-Host "ENTRY_TYPE:Solution"; Write-Host "ENTRY:$($sln.FullName)"
} else {
    $project = Get-ChildItem -Path $root -Filter "*.csproj" -Recurse -Depth 2 -ErrorAction SilentlyContinue |
        Select-Object -First 1
    if ($project) {
        Write-Host "ENTRY_TYPE:Project"; Write-Host "ENTRY:$($project.FullName)"
    } else {
        Write-Host "ENTRY_TYPE:NotFound"
    }
}

# Test projects: search path first, then git root, then parent
$searchRoots = @($root)
$gitRoot = (git -C $root rev-parse --show-toplevel 2>$null)
if ($gitRoot) { $gitRoot = [System.IO.Path]::GetFullPath($gitRoot) }
if ($gitRoot -and $gitRoot -ne $root) { $searchRoots += $gitRoot }
$parentPath = Split-Path $root -Parent
if ($parentPath -and $parentPath -ne $root -and $parentPath -ne $gitRoot) { $searchRoots += $parentPath }

$testProjects = @()
foreach ($sr in $searchRoots) {
    # Primary: match by .csproj content (test framework references)
    $testProjects = @(Get-ChildItem -Path $sr -Filter "*.csproj" -Recurse -Depth 5 -ErrorAction SilentlyContinue |
        Where-Object { $_.FullName -notmatch '([/\\]obj[/\\]|[/\\]bin[/\\])' } |
        Where-Object { (Select-String -Path $_.FullName -Pattern 'Microsoft\.NET\.Test\.Sdk|xunit|nunit|MSTest\.TestAdapter|"MSTest"|MSTest\.TestFramework|TUnit' -Quiet) })
    if ($testProjects.Count -gt 0) {
        if ($sr -ne $root) { Write-Host "SEARCHED:$sr" }
        break
    }
}

# Fallback: match by file name convention
if ($testProjects.Count -eq 0) {
    foreach ($sr in $searchRoots) {
        $testProjects = @(Get-ChildItem -Path $sr -Filter "*.csproj" -Recurse -Depth 5 -ErrorAction SilentlyContinue |
            Where-Object { $_.Name -match '(?i)(test|spec)' })
        if ($testProjects.Count -gt 0) {
            if ($sr -ne $root) { Write-Host "SEARCHED:$sr" }
            break
        }
    }
}
Write-Host "TEST_PROJECTS:$($testProjects.Count)"
$testProjects | ForEach-Object { Write-Host "TEST_PROJECT:$($_.FullName)" }

# Resolve the test output root (where coverage-analysis artifacts will be written)
if ($testProjects.Count -eq 0) {
    if ($gitRoot) {
        $testOutputRoot = $gitRoot
    } else {
        $testOutputRoot = $root
    }
} elseif ($testProjects.Count -eq 1) {
    $testOutputRoot = $testProjects[0].DirectoryName
} else {
    # Multiple test projects — find their deepest common parent directory
    $dirs = $testProjects | ForEach-Object { $_.DirectoryName }
    $common = $dirs[0]
    foreach ($d in $dirs[1..($dirs.Count-1)]) {
        $sep = [System.IO.Path]::DirectorySeparatorChar
        while (-not $d.StartsWith("$common$sep", [System.StringComparison]::OrdinalIgnoreCase) -and $d -ne $common) {
            $prevCommon = $common
            $common = Split-Path $common -Parent
            # Terminate if we can no longer move up (at filesystem root or no parent)
            if ([string]::IsNullOrEmpty($common) -or $common -eq $prevCommon) {
                $common = $null
                break
            }
        }
    }
    if ([string]::IsNullOrEmpty($common)) {
        # Fallback when no common parent directory exists (e.g., projects on different drives)
        if ($gitRoot) {
            $testOutputRoot = $gitRoot
        } else {
            $testOutputRoot = $root
        }
    } else {
        $testOutputRoot = $common
    }
}
Write-Host "TEST_OUTPUT_ROOT:$testOutputRoot"
  • If ENTRY_TYPE:NotFound and test projects were found → use the test projects directly as entry points (run dotnet test on each test .csproj).
  • If ENTRY_TYPE:NotFound and no test projects found → stop: No .sln or test projects found under <path>. Provide the path to your .NET solution or project.
  • If TEST_PROJECTS:0 and EXISTING_COBERTURA_COUNT > 0 (Step 2b) → continue with existing Cobertura XML analysis (no dotnet test run).
  • If TEST_PROJECTS:0 and EXISTING_COBERTURA_COUNT == 0 → stop: No test projects found (expected projects with 'Test' or 'Spec' in the name), and no existing Cobertura XML was provided. Add a test project or provide a Cobertura file path.
Step 2: Create the output directory
powershell
$coverageDir = Join-Path $testOutputRoot "TestResults" "coverage-analysis"
if (Test-Path $coverageDir) { Remove-Item $coverageDir -Recurse -Force }
New-Item -ItemType Directory -Path $coverageDir -Force | Out-Null
Write-Host "COVERAGE_DIR:$coverageDir"

This step only manages the TestResults/coverage-analysis/ subdirectory (skill-owned outputs). It must never delete user-supplied Cobertura files — those live one level up at TestResults/coverage.cobertura.xml (or wherever the user pointed). If the user provided a path that is TestResults/coverage-analysis/..., copy the file aside before this step recreates the directory.

Step 2b: Discover or accept existing Cobertura XML (required for the existing-data path)

If the user supplied a Cobertura XML path explicitly, use it. Otherwise probe well-known locations and any path the user mentioned:

powershell
# 1. Honor a user-supplied path first (highest priority)
$coberturaFiles = @()
if ($userSuppliedCoberturaPath -and (Test-Path $userSuppliedCoberturaPath)) {
    $coberturaFiles = @(Get-Item $userSuppliedCoberturaPath)
}

# 2. Otherwise scan TestResults/ at the repo/test root for any *.cobertura.xml
if ($coberturaFiles.Count -eq 0) {
    $searchPaths = @(
        (Join-Path $testOutputRoot "TestResults"),
        (Join-Path $root "TestResults")
    ) | Where-Object { $_ -and (Test-Path $_) } | Select-Object -Unique
    foreach ($sp in $searchPaths) {
        $found = @(Get-ChildItem -Path $sp -Filter "*.cobertura.xml" -Recurse -ErrorAction SilentlyContinue |
            Where-Object { $_.FullName -notmatch '[/\\]coverage-analysis[/\\]raw[/\\]' })
        if ($found.Count -gt 0) { $coberturaFiles = $found; break }
    }
}

Write-Host "EXISTING_COBERTURA_COUNT:$($coberturaFiles.Count)"
$coberturaFiles | ForEach-Object { Write-Host "EXISTING_COBERTURA:$($_.FullName)" }
  • If EXISTING_COBERTURA_COUNT > 0 → skip Phase 2 entirely and pass these paths to the Phase 3 scripts.
  • If EXISTING_COBERTURA_COUNT == 0 → run Phase 2 to generate fresh coverage; the file paths to feed Phase 3 will be discovered from <COVERAGE_DIR>/raw/ after dotnet test.
Step 2c: Recommend ignoring TestResults/
powershell
$pattern = "**/TestResults/"
$gitRoot = (git -C $testOutputRoot rev-parse --show-toplevel 2>$null)
if ($gitRoot) { $gitRoot = [System.IO.Path]::GetFullPath($gitRoot) }
if ($gitRoot) {
    $gitignorePath = Join-Path $gitRoot ".gitignore"
    $alreadyIgnored = $false
    if (Test-Path $gitignorePath) {
        $alreadyIgnored = (Select-String -Path $gitignorePath -Pattern '^\s*(\*\*/)?TestResults/?\s*$' -Quiet)
    }
    if ($alreadyIgnored) {
        Write-Host "GITIGNORE_RECOMMENDATION:already-present"
    } else {
        Write-Host "GITIGNORE_RECOMMENDATION:$pattern"
    }
} else {
    Write-Host "GITIGNORE_RECOMMENDATION:$pattern"
}
Phase 2 — Test execution (skip when Cobertura XML already exists)

Run only when no Cobertura XML is present. If the user already has coverage data, skip directly to Phase 3.

Step 3: Detect coverage provider and run dotnet test with coverage collection

Before running tests, detect which coverage provider the test projects use. Projects may reference Microsoft.Testing.Extensions.CodeCoverage (Microsoft's built-in provider, common on .NET 9+) or coverlet.collector (open-source, the default in xUnit templates). The provider determines which dotnet test arguments to use — both produce Cobertura XML.

powershell
# Detect coverage provider per test project
$coverageProvider = "unknown"  # will be set to "ms-codecoverage" or "coverlet"
$msCodeCovProjects = @()
$coverletProjects = @()
$neitherProjects = @()

foreach ($tp in $testProjects) {
    $hasMsCodeCov = Select-String -Path $tp.FullName -Pattern 'Microsoft\.Testing\.Extensions\.CodeCoverage' -Quiet
    $hasCoverlet = Select-String -Path $tp.FullName -Pattern 'coverlet\.collector' -Quiet
    if ($hasMsCodeCov) { $msCodeCovProjects += $tp }
    elseif ($hasCoverlet) { $coverletProjects += $tp }
    else { $neitherProjects += $tp }
}

# Determine the provider strategy
if ($msCodeCovProjects.Count -gt 0 -and $coverletProjects.Count -eq 0) {
    $coverageProvider = "ms-codecoverage"
    Write-Host "COVERAGE_PROVIDER:ms-codecoverage (ms:$($msCodeCovProjects.Count), none:$($neitherProjects.Count))"
} elseif ($coverletProjects.Count -gt 0 -and $msCodeCovProjects.Count -eq 0) {
    $coverageProvider = "coverlet"
    Write-Host "COVERAGE_PROVIDER:coverlet (coverlet:$($coverletProjects.Count), none:$($neitherProjects.Count))"
} elseif ($msCodeCovProjects.Count -gt 0 -and $coverletProjects.Count -gt 0) {
    $coverageProvider = "mixed-project"
    Write-Host "COVERAGE_PROVIDER:mixed-project (ms:$($msCodeCovProjects.Count), coverlet:$($coverletProjects.Count), none:$($neitherProjects.Count))"
} else {
    $coverageProvider = "coverlet"
    Write-Host "COVERAGE_PROVIDER:none-detected — defaulting to coverlet"
}

If any discovered test projects have no provider, add one based on the selected strategy:

powershell
if ($coverageProvider -eq "ms-codecoverage" -and $neitherProjects.Count -gt 0) {
    Write-Host "ADDING_MS_CODECOVERAGE:$($neitherProjects.Count) project(s)"
    foreach ($tp in $neitherProjects) {
        dotnet add $tp.FullName package Microsoft.Testing.Extensions.CodeCoverage --no-restore
        Write-Host "  ADDED_MS_CODECOVERAGE:$($tp.FullName)"
    }
    foreach ($tp in $neitherProjects) {
        dotnet restore $tp.FullName --quiet
    }
}

if (($coverageProvider -eq "coverlet" -or $coverageProvider -eq "mixed-project") -and $neitherProjects.Count -gt 0) {
    Write-Host "ADDING_COVERLET:$($neitherProjects.Count) project(s)"
    foreach ($tp in $neitherProjects) {
        dotnet add $tp.FullName package coverlet.collector --no-restore
        Write-Host "  ADDED:$($tp.FullName)"
    }
    foreach ($tp in $neitherProjects) {
        dotnet restore $tp.FullName --quiet
    }
}

Log each addition to the console so the developer sees what changed. Document the additions in the final report (see Output Format).

Run one dotnet test per entry point for the selected strategy:

  • In ms-codecoverage or coverlet mode: run a single command for the solution entry (or one per test project if no .sln was found).
  • In mixed-project mode: run one command per test project, using that project's existing provider to avoid dual-provider conflicts.

Coverlet (coverlet.collector):

powershell
$rawDir = Join-Path "<COVERAGE_DIR>" "raw"
dotnet test "<ENTRY>" `
    --collect:"XPlat Code Coverage" `
    --results-directory $rawDir `
    -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Format=cobertura `
    -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Include="[*]*" `
    -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Exclude="[*.Tests]*,[*.Test]*,[*Tests]*,[*Test]*,[*.Specs]*,[*.Testing]*" `
    -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.SkipAutoProps=true

Microsoft CodeCoverage (Microsoft.Testing.Extensions.CodeCoverage):

The command syntax depends on the .NET SDK version. In .NET 9, Microsoft.Testing.Platform arguments must be passed after the -- separator. In .NET 10+, --coverage is a top-level dotnet test flag.

powershell
$rawDir = Join-Path "<COVERAGE_DIR>" "raw"

# Detect SDK version for correct argument placement
$sdkVersion = (dotnet --version 2>$null)
$major = if ($sdkVersion -match '^(\d+)\.') { [int]$Matches[1] } else { 9 }

if ($major -ge 10) {
    # .NET 10+: --coverage is a first-class dotnet test flag
    dotnet test "<ENTRY>" `
        --results-directory $rawDir `
        --coverage `
        --coverage-output-format cobertura `
        --coverage-output $rawDir
} else {
    # .NET 9: pass Microsoft.Testing.Platform arguments after the -- separator
    dotnet test "<ENTRY>" `
        --results-directory $rawDir `
        -- --coverage --coverage-output-format cobertura --coverage-output $rawDir
}

Mixed-project mode (Microsoft.Testing.Extensions.CodeCoverage + coverlet.collector in the same solution):

powershell
$rawDir = Join-Path "<COVERAGE_DIR>" "raw"
$sdkVersion = (dotnet --version 2>$null)
$major = if ($sdkVersion -match '^(\d+)\.') { [int]$Matches[1] } else { 9 }

foreach ($tp in $testProjects) {
    $hasMsCodeCov = Select-String -Path $tp.FullName -Pattern 'Microsoft\.Testing\.Extensions\.CodeCoverage' -Quiet
    if ($hasMsCodeCov) {
        if ($major -ge 10) {
            dotnet test $tp.FullName --results-directory $rawDir --coverage --coverage-output-format cobertura --coverage-output $rawDir
        } else {
            dotnet test $tp.FullName --results-directory $rawDir -- --coverage --coverage-output-format cobertura --coverage-output $rawDir
        }
    } else {
        dotnet test $tp.FullName `
            --collect:"XPlat Code Coverage" `
            --results-directory $rawDir `
            -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Format=cobertura `
            -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Include="[*]*" `
            -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Exclude="[*.Tests]*,[*.Test]*,[*Tests]*,[*Test]*,[*.Specs]*,[*.Testing]*" `
            -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.SkipAutoProps=true
    }
}

Exit code handling:

  • 0 — all tests passed, coverage collected
  • 1 — some tests failed (coverage still collected — proceed with a warning)
  • Other — build failure; stop and report the error

After the run, locate coverage files:

powershell
$coberturaFiles = Get-ChildItem -Path (Join-Path "<COVERAGE_DIR>" "raw") -Filter "coverage.cobertura.xml" -Recurse
Write-Host "COBERTURA_COUNT:$($coberturaFiles.Count)"
$coberturaFiles | ForEach-Object { Write-Host "COBERTURA:$($_.FullName)" }
$vsCovFiles = Get-ChildItem -Path (Join-Path "<COVERAGE_DIR>" "raw") -Filter "*.coverage" -Recurse -ErrorAction SilentlyContinue
if ($vsCovFiles) { Write-Host "VS_BINARY_COVERAGE:$($vsCovFiles.Count)" }

If COBERTURA_COUNT is 0:

  • If VS_BINARY_COVERAGE > 0: warn the user — "Found .coverage files (VS binary format) but no Cobertura XML. These were likely produced by Visual Studio's built-in collector, which outputs a binary format by default. This skill needs Cobertura XML. Re-running with the detected provider configured for Cobertura output." Then re-run the appropriate dotnet test command above (Coverlet or Microsoft CodeCoverage) with Cobertura format.
  • If no .coverage files either: stop and report — "Coverage files not generated. Ensure dotnet test completed successfully and check the build output for errors."
Phase 3 — Analysis (sequential)

Run the two bundled PowerShell scripts. Both are cheap and complete in seconds. Do not install or invoke ReportGenerator here — that belongs in optional Phase 5, after the user-facing summary has been delivered.

Show full SKILL.md (835 more words)Show less
Step 4: Calculate CRAP scores using the bundled script

Run scripts/Compute-CrapScores.ps1 (co-located with this SKILL.md). It reads all Cobertura XML files, applies CRAP(m) = comp² × (1 − cov)³ + comp per method, and returns the top-N hotspots as JSON.

To locate the script: find the directory containing this skill's SKILL.md file (the skill loader provides this context), then resolve scripts/Compute-CrapScores.ps1 relative to it. If the script path cannot be determined, calculate CRAP scores inline using the formula below.

powershell
& "<skill-directory>/scripts/Compute-CrapScores.ps1" `
    -CoberturaPath @(<all COBERTURA file paths as array>) `
    -CrapThreshold <crap_threshold> `
    -TopN <top_n>

Script outputs: OVERALL_LINE_COVERAGE:<n>, OVERALL_BRANCH_COVERAGE:<n> (aggregated project-wide rates across all provided Cobertura files), TOTAL_METHODS:<n>, FLAGGED_METHODS:<n>, HOTSPOTS:<json> (top-N sorted by CrapScore descending). The OVERALL_* values are exactly what the Phase 4 summary needs for the "Line Coverage" / "Branch Coverage" rows — no separate XML parsing tool call is required.

Step 5: Extract per-method coverage gaps

Run scripts/Extract-MethodCoverage.ps1 to get per-method coverage data for the Coverage Gaps table:

powershell
& "<skill-directory>/scripts/Extract-MethodCoverage.ps1" `
    -CoberturaPath @(<all COBERTURA file paths as array>) `
    -CoverageThreshold <line_threshold> `
    -BranchThreshold <branch_threshold> `
    -Filter below-threshold

Script outputs: JSON array of methods below the coverage threshold, sorted by coverage ascending. Use this data to populate the Coverage Gaps by File table in the report.

Phase 4 — User-facing summary (MANDATORY — your next assistant response)

As soon as Phase 3 completes, your immediately next assistant response must contain the user-facing analysis — do not interleave any other tool calls before it. This is the response the user (and any judge) sees. Skipping or deferring this in favor of Phase 5 (ReportGenerator) is a hard failure.

The response must include, at minimum:

  1. Overall line and branch coverage — read directly from the OVERALL_LINE_COVERAGE: / OVERALL_BRANCH_COVERAGE: lines emitted by Compute-CrapScores.ps1 (no extra Cobertura parsing required)
  2. The Risk Hotspots table built from Compute-CrapScores.ps1 HOTSPOTS: output (CRAP scores, complexity, coverage)
  3. Identification of the highest-risk method(s) and what is blocking coverage
  4. 1–3 prioritized, specific recommendations (which method to test, expected CRAP/coverage impact)

Use references/output-format.md verbatim for fixed headings, table structures, symbols, and emoji. Use references/guidelines.md for prioritization rules and style.

If Phase 5 has not yet run when you compose this summary, mark the ## 📁 Reports section's HTML/Text/CSV/GitHub-markdown rows as Not generated (optional — request HTML reports to enable). Only the coverage-analysis.md and raw Cobertura paths are guaranteed to exist.

Attempt to save the same content to TestResults/coverage-analysis/coverage-analysis.md before delivering the response (use the editor's create/edit tool — do not shell out). If the file write fails, still deliver the summary and note the file-write failure explicitly.

Phase 5 — Optional: ReportGenerator HTML/CSV reports (post-summary)

Phase 5 is strictly optional and runs only after Phase 4 has been delivered. Skip Phase 5 entirely when:

  • The user supplied existing Cobertura XML and only asked for analysis (the default for the existing-data path).
  • The user is diagnosing a coverage plateau or asking "what's blocking me?" — they want the answer, not a static-site report.
  • ReportGenerator is not already installed and you have no clear signal the user wants HTML reports.

Run Phase 5 only when the user explicitly asks for HTML/CSV reports, or when the project flow requires them (e.g., a CI artifact upload step).

Step 6: Verify or install ReportGenerator (only if running Phase 5)
powershell
$rgAvailable = $false
$rgCommand = Get-Command reportgenerator -ErrorAction SilentlyContinue
if ($rgCommand) {
    $rgAvailable = $true
    Write-Host "RG_INSTALLED:already-present"
} else {
    $rgToolPath = Join-Path "<COVERAGE_DIR>" ".tools"
    dotnet tool install dotnet-reportgenerator-globaltool --tool-path $rgToolPath
    if ($LASTEXITCODE -eq 0) {
        $env:PATH = "$rgToolPath$([System.IO.Path]::PathSeparator)$env:PATH"
        $rgCommand = Get-Command reportgenerator -ErrorAction SilentlyContinue
        if ($rgCommand) {
            $rgAvailable = $true
            Write-Host "RG_INSTALLED:true (tool-path: $rgToolPath)"
        } else {
            Write-Host "RG_INSTALLED:false"
            Write-Host "RG_INSTALL_ERROR:reportgenerator-not-available"
        }
    } else {
        Write-Host "RG_INSTALLED:false"
        Write-Host "RG_INSTALL_ERROR:reportgenerator-not-available"
    }
}
Write-Host "RG_AVAILABLE:$rgAvailable"

If installation fails (no internet), keep RG_AVAILABLE:false, leave the existing user-facing summary as the final output, and note that HTML reports were skipped.

Step 7: Generate HTML/CSV reports
powershell
$reportsDir = Join-Path "<COVERAGE_DIR>" "reports"
if ($rgAvailable) {
    reportgenerator `
        -reports:"<semicolon-separated COBERTURA paths>" `
        -targetdir:$reportsDir `
        -reporttypes:"Html;TextSummary;MarkdownSummaryGithub;CsvSummary" `
        -title:"Coverage Report" `
        -tag:"coverage-analysis-skill"

    Get-Content (Join-Path $reportsDir "Summary.txt") -ErrorAction SilentlyContinue
} else {
    Write-Host "REPORTGENERATOR_SKIPPED:true"
}

After Phase 5 completes successfully, you may follow up with a short message pointing the user to the generated HTML report (one paragraph, no need to repeat the summary).

Validation

  • Verify that at least one coverage.cobertura.xml file was generated after dotnet test (or already exists when the user supplied one)
  • Confirm the assistant response contained the CRAP/risk-hotspot table — saving the markdown file is secondary
  • Confirm TestResults/coverage-analysis/coverage-analysis.md was written and contains data
  • Spot-check one method's CRAP score: comp² × (1 − cov)³ + comp — a method with 100% coverage should have CRAP = complexity
  • If Phase 5 ran, verify TestResults/coverage-analysis/reports/index.html exists; otherwise the report file should mark HTML/Text/CSV rows as Not generated

Common Pitfalls

  • No Cobertura XML generated — the test project may lack a coverage provider. The skill auto-adds one, but if dotnet add package fails (offline/proxy), coverage collection silently produces nothing. Check for .coverage binary files as a fallback indicator.
  • Test failures (exit code 1) — coverage is still collected from passing tests. Do not abort; proceed with partial data and note the failures in the summary.
  • Premature end before user-facing summary — never start Phase 5 (ReportGenerator install/run) before the Phase 4 assistant response is delivered. The heavy dotnet tool install can crash the session or exhaust budget, leaving the user with no analysis even though the CRAP scores were already computed.
  • ReportGenerator install failure — if dotnet tool install fails (no internet) during Phase 5, leave the existing Phase 4 summary as the final output and note that HTML reports were skipped. Do not retry or block on the install.
  • Method name mismatches in Cobertura — async methods, lambdas, and local functions may have compiler-generated names. The scripts use the Cobertura method name/signature directly; verify against source if results look unexpected.
  • Mixed coverage providers — when a solution contains both Coverlet and Microsoft CodeCoverage projects, the skill runs per-project to avoid dual-provider conflicts. This is slower but correct.

© microsoft, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 4 other files (scripts, references) in .agents/skills/coverage-analysis of microsoft/testfx.

  • SKILL.md
  • references/guidelines.md
  • references/output-format.md
  • scripts/Compute-CrapScores.ps1
  • scripts/Extract-MethodCoverage.ps1

Open the folder on GitHubat commit 44b9dcc

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Works with

Categories

Questions about Coverage Analysis

What does Coverage Analysis do?

Project-wide code coverage and CRAP (Change Risk Anti-Patterns) score analysis for .NET projects. Coverage Analysis is an agent skill from microsoft/testfx, published by the product's own GitHub organization.NET projects.

When should I use Coverage Analysis?

Coverage Analysis fits situations like: diagnose why coverage is stuck; identify what methods block improvement; get project-wide coverage analysis with risk ranking; : coverage stuck.

How do I install Coverage Analysis in Claude Code?

Run `npx skills add microsoft/testfx --skill coverage-analysis -a claude-code`. Or copy the skill folder (.agents/skills/coverage-analysis in microsoft/testfx) into .claude/skills/coverage-analysis in your project. Claude Code loads it when a task matches its description.

How do I install Coverage Analysis in Codex?

Run `npx skills add microsoft/testfx --skill coverage-analysis -a codex`. Or copy the skill folder (.agents/skills/coverage-analysis in microsoft/testfx) into .agents/skills/coverage-analysis in your project. Codex loads it when a task matches its description.

Can I use Coverage Analysis in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add microsoft/testfx --skill coverage-analysis -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/coverage-analysis, .gemini/skills/coverage-analysis, .github/skills/coverage-analysis and .opencode/skills/coverage-analysis in your project.

What does Coverage Analysis need to run?

Going by SKILL.md and its folder, Coverage Analysis needs PowerShell for the scripts in its folder and the command-line tools its instructions call (dotnet). Our summary lists: PowerShell.

Does Coverage Analysis access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Coverage Analysis safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. The check reads SKILL.md only: the scripts in the folder are not scanned, so read them before running anything.

What licence does Coverage Analysis use?

Coverage Analysis is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Coverage Analysis use?

About 7.3k tokens (SKILL.md is roughly 29k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 2.2k tokens, read only when the agent opens those files.

What are the alternatives to Coverage Analysis?

Skills that share tags, products or a category with Coverage Analysis: Evaluate PR Tests (dotnet/maui, 23k stars), Find Untested Sources (dotnet/skills, 5.6k stars), Coverage Analysis (runceel/ReactiveProperty, 944 stars) and Stryker Dotnet (ardalis/RiverBooks, 134 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Coverage Analysis?

microsoft (a GitHub organization, an official publisher) maintains it in microsoft/testfx, which has 1,047 GitHub stars. The repository holds 44 skills in this directory. The repository was last updated on October 7, 2026.

Source: microsoft/testfx on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.