CoverageRatchet

Per-file code coverage enforcement that only goes up. CoverageRatchet reads your Cobertura XML coverage reports, compares each file against its threshold, and helps prevent coverage from regressing.

How It Works

Your test suite generates a Cobertura XML coverage report (most .NET coverage tools support this format).
CoverageRatchet reads the report and compares each file's line and branch coverage against its threshold.
*check* fails the build if any file drops below its threshold.
*ratchet* (the default command) updates thresholds to match current coverage -- thresholds only go up, not down.
*loosen* sets thresholds to whatever coverage is right now, so check passes immediately.
*targets* lists files sorted by coverage to find improvement opportunities.
*gaps* shows uncovered branch points per file with line numbers.

The default threshold for every file is 100% line and branch coverage. Files that can't easily reach 100% (like CLI entry points) can get per-file overrides with a documented reason.

Installation

dotnet tool install -g CoverageRatchet

Usage

Ratchet (default)

Just run coverageratchet with no arguments to ratchet thresholds upward:

coverageratchet

This recursively searches for a coverage.cobertura.xml file, compares each file against its threshold, and tightens thresholds where coverage has improved. Exit codes:

Exit code	Meaning
0	All thresholds met, no config changes needed
1	Config was updated (some thresholds tightened)
2	Some files are below their threshold

You can also run it explicitly as coverageratchet ratchet.

Check coverage (CI)

coverageratchet check

Exits with code 0 if all files meet their thresholds, 1 if any file is below.

Loosen thresholds

If you need check to pass right now (e.g., after a big refactor that dropped coverage), loosen sets every file's threshold to its current actual coverage:

coverageratchet loosen

This always exits 0. Files that were already at 100% don't get an override. New overrides get the reason "loosened automatically".

Show improvement targets

coverageratchet targets

Lists all files sorted by line coverage (lowest first), so you can see where to focus testing effort. Always exits 0.

Show branch coverage gaps

coverageratchet gaps

Shows uncovered branch points per file, with specific line numbers and how many branches are covered vs total. Files are sorted by gap count (most gaps first). Always exits 0.

Export coverage as JSON (for CI)

coverageratchet check-json [config-path] [output-path]

Writes machine-readable coverage results. Exit code matches check (non-zero if any file fails). Used by CI workflows to upload coverage data as an artifact.

Sync thresholds from CI

coverageratchet loosen-from-ci [config-path]

Pushes current code, polls CI, and if coverage fails: 1. Downloads the coverage-thresholds artifact 2. Merges CI platform thresholds into local config (splitting non-platform entries if needed) 3. Commits, pushes, and re-polls CI

Requires gh CLI and jj (or git).

Artifact contract

loosen-from-ci expects CI to upload an artifact named coverage-thresholds containing one file per project: coverage-thresholds-<project>.json. Each file is the output of check-json with shape:

{
  "platform": "linux",
  "results": {
    "Foo.fs": { "line": 72, "branch": 54 },
    "Bar.fs": { "line": 80, "branch": 100 }
  }
}

platform is one of linux, macos, windows. <project> matches the suffix of the local coverage-ratchet-<project>.json config; files named coverage-thresholds-default.json (or coverage-thresholds-.json) merge into the default coverage-ratchet.json config. The reusable build workflow michaels-wacky-build.yml produces this artifact automatically.

Partial-run survival with baselines

If your test runner only runs a subset of tests (e.g. a test-impact analyzer like fs-hot-watch's TestPrune runs only tests affected by your changes), the coverage XML from that partial run will reflect only the lines touched by that subset. Lines covered by tests that didn't re-run show zero hits. Coverage appears to drop; check fails even though nothing regressed.

CoverageRatchet can guard against this by merging each run onto a per-project baseline — a snapshot of the last full run. Merging takes the max hits per line across baseline and current, so partial runs can only raise coverage, never lower it.

Layout — per test project:

coverage/<project>/
  coverage.baseline.xml   # last full run; source of truth
  coverage.cobertura.xml  # what check reads; merged after every run

Flow:

# Before each check, layer baseline onto current run. Bootstraps baseline
# on the first run automatically if it doesn't exist yet.
coverageratchet --search-dir coverage check --merge-baselines

# After a deliberate *full* test run (no impact filter), advance baseline:
coverageratchet --search-dir coverage refresh-baseline

If FSHW_RAN_FULL_SUITE=true is set when check --merge-baselines runs AND the check passes, the baseline is refreshed automatically — useful when a test runner can tell you whether it just ran the full suite.

One-shot merge — for ad-hoc merges outside the standard layout:

coverageratchet merge <baseline.xml> <partial.xml> <output.xml>

Gotchas:

Deleted tests leave stale hits in the baseline until it's refreshed. If you delete a test that was the only one covering some lines, those lines keep their old hit counts until refresh-baseline runs. Budget a periodic full run (daily CI, for example) to catch this.
New source files added in a partial-only run are measured only by whichever tests ran — that's all the merger knows about. Ratchet thresholds for new files will reflect partial coverage until the next full run refreshes the baseline.
Baselines are a safety net against false drops, not a substitute for periodic full runs.

Custom search directory

By default, CoverageRatchet recursively searches . for coverage files. Use --search-dir to search a different directory:

coverageratchet --search-dir coverage check
coverageratchet check --search-dir coverage

The flag works in any position. Directories like .devenv are automatically skipped to avoid slow traversal of Nix store symlinks.

Custom config path

coverageratchet check path/to/my-config.json
coverageratchet ratchet path/to/my-config.json
coverageratchet loosen path/to/my-config.json

Configuration

CoverageRatchet uses a JSON config file (default: coverage-ratchet.json in the current directory).

Example `coverage-ratchet.json`

{
  "overrides": {
    "Program.fs": {
      "line": 85.5,
      "branch": 77.0,
      "reason": "CLI entry point -- exit calls are not coverable"
    },
    "Api.fs": {
      "line": 92.38,
      "branch": 73.33,
      "reason": "Reflection branches generated by compiler"
    }
  }
}

Config fields

Field	Type	Description
`overrides`	object	Per-file threshold overrides, keyed by filename
`overrides.<file>.line`	number	Minimum line coverage percentage (0-100)
`overrides.<file>.branch`	number	Minimum branch coverage percentage (0-100)
`overrides.<file>.reason`	string	Why this file has a lower threshold
`overrides.<file>.platform`	string	Optional: `"macos"`, `"linux"`, or `"windows"` — restricts this override to one platform

Files not listed in overrides must have 100% line and branch coverage.

Platform-specific overrides

When coverage differs across platforms (e.g., OS-specific code paths), a file's override can be an array of platform-specific entries instead of a single object:

{
  "overrides": {
    "Program.fs": [
      { "line": 79, "branch": 76, "reason": "CLI entry point", "platform": "macos" },
      { "line": 46, "branch": 44, "reason": "CLI entry point", "platform": "linux" }
    ]
  }
}

Resolution rules: - If an entry matches the current platform, it is used. - Otherwise, a platform-agnostic entry (no platform field) is used as fallback. - If no entry matches, the file defaults to 100%/100%.

The loosen command creates platform-agnostic overrides for new files. Only loosen-from-ci introduces platform-specific entries, since it integrates coverage results from CI runners on different platforms.

Multi-platform workflow

When loosen-from-ci writes a single-platform entry (e.g. linux), the default 100%/100% threshold still applies to other platforms for that file. Running check locally on a platform without an entry will fail — even if actual coverage is high — because 95% < 100%.

The fix is to run loosen locally to add the matching platform entry from your actual coverage:

#CI (linux) fails on Foo.fs 
#On your macOS dev machine, `check` now fails because there's no macos entry 
coverageratchet loosen coverage-ratchet-<project>.json
#macOS entry added from actual local coverage.
#Later, once tests improve actual coverage on both platforms:
coverageratchet ratchet coverage-ratchet-<project>.json
#Both entries tightened to current numbers.

ratchet only tightens existing entries — it won't synthesize a new platform entry. That's loosen's job. This keeps the split of responsibilities clean: loosen-from-ci pins the CI platform at release time, loosen pins the dev platform on demand, ratchet tightens both as coverage goes up.

Example Output

  Program.fs: line 87.2% >= 85.5% PASS | branch 80.0% >= 77.0% PASS
  Sync.fs:    line 100%  >= 100%  PASS | branch 100%  >= 100%  PASS
  Api.fs:     line 90.0% >= 92.38% FAIL | branch 75.0% >= 73.33% PASS

Typical CI Setup

Run your tests with coverage enabled (e.g., dotnet test --collect:"XPlat Code Coverage")
Run coverageratchet check to enforce thresholds
Run coverageratchet locally after improving tests to lock in coverage gains

License

MIT