<h1 align="center">
<strong>dev-coverage</strong>
<br>
<sup><sub>TEST COVERAGE FOR RUST</sub></sup>
</h1>
<p align="center">
<a href="https://crates.io/crates/dev-coverage"><img alt="crates.io" src="https://img.shields.io/crates/v/dev-coverage.svg"></a>
<a href="https://crates.io/crates/dev-coverage"><img alt="downloads" src="https://img.shields.io/crates/d/dev-coverage.svg"></a>
<a href="https://docs.rs/dev-coverage"><img alt="docs.rs" src="https://docs.rs/dev-coverage/badge.svg"></a>
<a href="https://github.com/jamesgober/dev-coverage/actions/workflows/ci.yml"><img alt="CI" src="https://github.com/jamesgober/dev-coverage/actions/workflows/ci.yml/badge.svg"></a>
<img alt="MSRV" src="https://img.shields.io/badge/msrv-1.85%2B-blue.svg?style=flat-square" title="Rust Version">
</p>
<p align="center">
Test coverage measurement and regression detection.<br>
Part of the <code>dev-*</code> verification suite.
</p>
---
## What it does
`dev-coverage` drives [`cargo-llvm-cov`](https://github.com/taiki-e/cargo-llvm-cov)
against your project, parses the JSON output, and emits results as a
[`dev-report::Report`](https://docs.rs/dev-report). It compares against a
stored baseline to flag regressions so AI agents and CI gates can act
without parsing free-form text.
## Why a separate crate
Test coverage is the single most direct way to ask "how much of this
code is actually exercised?" Without it, every other quality check is
an opinion. With it, you can answer "did this PR drop line coverage
below 80%?" or "did this PR introduce a 5-point regression vs. main?"
as a yes/no decision.
`dev-coverage` makes those questions programmable, not interactive.
## Quick start
```toml
[dependencies]
dev-coverage = "0.9"
```
One-time tool install:
```bash
cargo install cargo-llvm-cov
```
Drive it from code:
```rust,no_run
use dev_coverage::{CoverageRun, CoverageThreshold};
let run = CoverageRun::new("my-crate", "0.1.0");
let result = run.execute()?;
let threshold = CoverageThreshold::min_line_pct(80.0);
let check = result.into_check_result(threshold);
// `check` is a `dev_report::CheckResult` ready to push into a Report.
# Ok::<(), dev_coverage::CoverageError>(())
```
## Threshold types
| `CoverageThreshold::MinLinePct` | Percent of executable lines exercised by tests. |
| `CoverageThreshold::MinFunctionPct`| Percent of functions called by at least one test. |
| `CoverageThreshold::MinRegionPct` | Percent of basic blocks (branch points) exercised. |
Line coverage is the most common. Region coverage is the strictest.
## Baseline workflow
The headline feature beyond raw measurement: persist a baseline, then
flag regressions on the next run.
```rust,no_run
use dev_coverage::{
Baseline, BaselineStore, CoverageRun, JsonFileBaselineStore,
};
let run = CoverageRun::new("my-crate", "0.1.0");
let result = run.execute()?;
let store = JsonFileBaselineStore::new("coverage-baselines");
// Compare against last run on main.
if let Some(baseline) = store.load("main", "my-crate")? {
let diff = result.diff(&baseline, /* tolerance_pct */ 1.0);
if diff.regressed {
eprintln!(
"coverage regressed: line {:+.2}pp, function {:+.2}pp, region {:+.2}pp",
diff.line_pct_delta,
diff.function_pct_delta,
diff.region_pct_delta,
);
}
}
// Persist for next time.
store.save("main", &result.to_baseline())?;
# Ok::<(), Box<dyn std::error::Error>>(())
```
`JsonFileBaselineStore` writes one `<root>/<scope>/<name>.json` per
baseline with atomic write-temp-rename semantics; a partial write that
survives a crash will not corrupt the comparison on the next run.
## `Producer` integration
`CoverageProducer` plugs coverage into a multi-producer pipeline driven
by [`dev-tools`](https://github.com/jamesgober/dev-tools):
```rust,no_run
use dev_coverage::{CoverageProducer, CoverageRun, CoverageThreshold};
use dev_report::Producer;
let producer = CoverageProducer::new(
CoverageRun::new("my-crate", "0.1.0"),
CoverageThreshold::min_line_pct(80.0),
);
let report = producer.produce();
println!("{}", report.to_json().unwrap());
```
When a baseline is wired in via `with_baseline`, the producer pushes a
second `CheckResult` named `coverage::regression::<subject>` carrying
the deltas in its `detail` field, with verdict `Fail (Error)` if the
regression exceeds the tolerance.
## Examples
| `examples/basic.rs` | Run coverage against the current crate; emit a `CheckResult`. |
| `examples/with_threshold.rs` | Every `CoverageThreshold` variant against a constructed result. |
| `examples/baseline.rs` | Save a baseline, then diff a new run against it. |
| `examples/producer.rs` | Wrap a run in `CoverageProducer` (gated by `DEV_COVERAGE_EXAMPLE_RUN`). |
## Requirements
[`cargo-llvm-cov`](https://github.com/taiki-e/cargo-llvm-cov) must be
installed on the system. The crate detects absence and surfaces a
`CoverageError::ToolNotInstalled` rather than panicking.
```bash
cargo install cargo-llvm-cov
```
The crate's own dependency footprint is small: `dev-report`, `serde`,
`serde_json`.
## Migration from `0.1.0`
`CoverageResult` gained `branch_pct`, `total_functions`,
`covered_functions`, `total_regions`, `covered_regions`, and `files`.
If you constructed `CoverageResult` literals in `0.1.0`, fill in the
new fields:
```rust
# use dev_coverage::CoverageResult;
let _r = CoverageResult {
name: "x".into(),
version: "0.1.0".into(),
line_pct: 85.0,
function_pct: 90.0,
region_pct: 80.0,
// new in 0.9.0:
branch_pct: None,
total_lines: 100,
covered_lines: 85,
total_functions: 20,
covered_functions: 18,
total_regions: 50,
covered_regions: 40,
files: Vec::new(),
};
```
The constructor surface (`CoverageRun::new`, `CoverageThreshold::min_*`,
`CoverageResult::into_check_result`) is unchanged.
## The `dev-*` suite
See [`dev-tools`](https://github.com/jamesgober/dev-tools) for the
umbrella crate covering the full suite.
## Status
`v0.9.x` is the pre-1.0 stabilization line. The API is feature-complete
for coverage measurement, baseline storage, and regression detection.
Production use is fine; `1.0` will pin the public API and the wire
format.
## Minimum supported Rust version
`1.85` — pinned in `Cargo.toml` via `rust-version` and verified by the
MSRV job in CI.
## License
Apache-2.0. See [LICENSE](LICENSE).