/find-untested-sources

name: find-untested-sources
description: >
  MANDATORY for static requests to find, identify, or list untested source files
  or modules, sources without tests, source-to-test pairing, test-gap worklists,
  or suggested test locations. Invoke even for a tiny package; do not substitute
  manual globbing. Uses Roslyn for C#/.NET and tree-sitter for Python, TS/JS, Go,
  Java, Rust, and Ruby. DO NOT USE FOR: line/branch coverage, CRAP risk, or
  grading existing tests.
license: MIT

Find Untested Sources

Purpose

Coverage tools answer "which lines were executed?" — they require a green build and a passing test run, which is minutes-to-tens-of-minutes on a real repo. The question this skill answers is different and much cheaper:

> _Which source files have no test file referencing any of their declared > types/symbols?_

That's the question an agent asks **before** writing a new test — and it can be answered statically in a few seconds by parsing source files, with **no build, no dependency resolution, and no compilation**. The output is a deterministic test-pairing map that lets the agent pick the next file to test without reading the entire codebase first.

Two engines — pick one

This skill ships two interchangeable analyzers with a compatible JSON contract:

| Engine | Script | Use when | |--------|--------|----------| | **Roslyn (C#)** | `scripts/Find-UntestedSources.cs` | The repo is **.NET-only**. Parses every `.cs` file with the Roslyn syntax API and does strict **namespace disambiguation**, so it is materially more accurate on duplicated short names like `Settings` or `Context`. | | **tree-sitter (polyglot)** | `scripts/find_untested_sources.py` | The repo is **not exclusively C#**, or you want one tool across Python, TypeScript/JavaScript, Go, Java, Rust, Ruby, and C#. |

For a .NET-only repository, **prefer the Roslyn engine** — its namespace-aware pairing beats the polyglot engine's identifier overlap.

Required workflow

1. Use the narrowest repository or package root named by the caller. Do not scan a parent workspace when the request identifies a subdirectory. 2. Execute the appropriate analyzer once. Do not replace analyzer execution with manual globbing, filename matching, or visual inspection. For polyglot analysis, pass `--include-tested` when the answer must distinguish paired sources from unpaired sources. 3. Base the result on the analyzer's JSON. Preserve its paired/unpaired classification and suggested relative path; do not guess a different path. 4. When the caller named a subdirectory, prefix analyzer-relative paths with that subdirectory so reported paths are workspace-relative. 5. Report the requested result plus the static-pairing coverage caveat. Do not append build, package-install, test-run, or coverage commands. When paired sources exist, name their covering test files so the unpaired classification is auditable.

When to Use

• User asks "where should I add tests?", "which files have no tests?", "find

untested code", "give me a test gap list", "what's the next file to test".

• Before invoking a test-generation agent, to produce a prioritized worklist.
• After generating tests, to verify each new test file pairs to a source file.
• To enumerate "weakly paired" source files (only one referring test) for

follow-up depth checks.

When Not to Use

• **Line/branch coverage** — use `coverage-analysis`.
• **CRAP-score / risk hotspots** — use `coverage-analysis`.
• **Are existing tests strong?** — use `test-gap-analysis` (mutation reasoning)

or `assertion-quality`.

Roslyn engine (C#)

Prerequisites

• .NET SDK that supports file-based apps (`dotnet run script.cs`). Pinned in the

repo's `global.json` (SDK 11 preview or later).

• No internet access required beyond the initial NuGet restore of

`Microsoft.CodeAnalysis.CSharp` on first run.

Usage

# From the skill folder
dotnet run scripts/Find-UntestedSources.cs -- <repo-root> [--top N]

# Save the report
dotnet run scripts/Find-UntestedSources.cs -- <repo-root> > pairing.json

# Iterate the untested list, highest-API-surface first
$report = Get-Content pairing.json | ConvertFrom-Json
$report.untested | Select-Object -First 10 source, decl_count, suggested_test_path

Diagnostics go to stderr; JSON goes to stdout.

Output schema

{
  "repo": "<absolute path>",
  "elapsed_ms": 8883,
  "counts": {
    "source_files": 3036,
    "test_files": 867,
    "untested_files": 1852,
    "paired_files": 1184
  },
  "untested": [
    {
      "source": "src/Foo/Bar.cs",
      "decl_count": 8,            // # of type declarations in the file
      "suggested_test_path":      // mirror of source under a discovered test project
        "tests/Foo.Tests/Bar/BarTests.cs"
    }
  ],
  "source_to_tests": {
    "src/Foo/Baz.cs": [
      "tests/Foo.Tests/BazTests.cs",
      "tests/Foo.IntegrationTests/Scenarios/BazScenarios.cs"
    ]
  }
}

How it works

1. **File discovery** — recursive walk pruning `bin/`, `obj/`, `node_modules/`, `.git/`, `.vs/`, `packages/`, and any dotted subdir. Skips generated files (`.g.cs`, `.Designer.cs`, `.AssemblyInfo.cs`). 2. **Test vs source classification** — walks up to the nearest `.csproj` and marks it a test project if the project name ends in `.Tests`, `.Test`, `.UnitTests`, `.IntegrationTests`, `.E2E`, `.EndToEnd`, `.Spec`, `.Specs`, or the content references `Microsoft.NET.Test.Sdk`, `MSTest.Sdk`, `Microsoft.Testing.Platform`, `xunit`, `NUnit`, `TUnit`, or `<IsTestProject>true</IsTestProject>`. 3. **Source index (parallel)** — parse each source file with `CSharpSyntaxTree.ParseText` (syntax only, no compilation); record every `BaseTypeDeclarationSyntax` / `DelegateDeclarationSyntax` as `(ShortName, EnclosingNamespace, FilePath)`. 4. **Test scan (parallel)** — parse each test file, collect `using` directives + enclosing namespace, walk every `IdentifierToken`, loo