Code Coverage — Seeing What Tests Miss 🟢

# Installcargo install cargo-llvm-cov# Or via rustup component (for the raw llvm tools)rustup component add llvm-tools-preview

# Run tests and show per-file coverage summarycargo llvm-cov# Generate HTML report (browseable, line-by-line highlighting)cargo llvm-cov --html# Output: target/llvm-cov/html/index.html# Generate LCOV format (for CI integrations)cargo llvm-cov --lcov --output-path lcov.info# Workspace-wide coverage (all crates)cargo llvm-cov --workspace# Include only specific packagescargo llvm-cov --package accel_diag --package topology_lib# Coverage including doc testscargo llvm-cov --doctests

# Installcargo install cargo-tarpaulin# Basic coverage reportcargo tarpaulin# HTML outputcargo tarpaulin --out Html# With specific optionscargo tarpaulin \    --workspace \    --timeout 120 \    --out Xml Html \    --output-dir coverage/ \    --exclude-files "*/tests/*" "*/benches/*" \    --ignore-panics# Skip certain cratescargo tarpaulin --workspace --exclude diag_tool  # exclude the binary crate

# Installcargo install grcov# Step 1: Build with coverage instrumentationexport RUSTFLAGS="-Cinstrument-coverage"export LLVM_PROFILE_FILE="target/coverage/%p-%m.profraw"cargo build --tests# Step 2: Run tests (generates .profraw files)cargo test# Step 3: Aggregate with grcovgrcov target/coverage/ \    --binary-path target/debug/ \    --source-dir . \    --output-types html,lcov \    --output-path target/coverage/report \    --branch \    --ignore-not-existing \    --ignore "*/tests/*" \    --ignore "*/.cargo/*"# Step 4: View reportopen target/coverage/report/html/index.html

# .github/workflows/coverage.ymlname: Code Coverageon: [push, pull_request]jobs:  coverage:    runs-on: ubuntu-latest    steps:      - uses: actions/checkout@v4      - uses: dtolnay/rust-toolchain@stable        with:          components: llvm-tools-preview      - name: Install cargo-llvm-cov        uses: taiki-e/install-action@cargo-llvm-cov      - name: Generate coverage        run: cargo llvm-cov --workspace --lcov --output-path lcov.info      - name: Upload to Codecov        uses: codecov/codecov-action@v4        with:          files: lcov.info          token: ${{ secrets.CODECOV_TOKEN }}          fail_ci_if_error: true      # Optional: enforce minimum coverage      - name: Check coverage threshold        run: |          cargo llvm-cov --workspace --fail-under-lines 80          # Fails the build if line coverage drops below 80%

# Get per-crate coverage as JSONcargo llvm-cov --workspace --json | jq '.data[0].totals.lines.percent'# Fail if below thresholdcargo llvm-cov --workspace --fail-under-lines 80cargo llvm-cov --workspace --fail-under-functions 70cargo llvm-cov --workspace --fail-under-regions 60

// 100% line coverage, 50% branch coverage — still risky!
pub fn classify_temperature(temp_c: i32) -> ThermalState {
    if temp_c > 105 {       // ← tested with temp=110 → Critical
        ThermalState::Critical
    } else if temp_c > 85 { // ← tested with temp=90 → Warning
        ThermalState::Warning
    } else if temp_c < -10 { // ← NEVER TESTED → sensor error case missed
        ThermalState::SensorError
    } else {
        ThermalState::Normal  // ← tested with temp=25 → Normal
    }
}

# Exclude test code from coverage (it's always "covered")cargo llvm-cov --workspace --ignore-filename-regex 'tests?\.rs$|benches/'# Exclude generated codecargo llvm-cov --workspace --ignore-filename-regex 'target/'

// Coverage tools recognize this pattern
#[cfg(not(tarpaulin_include))]  // tarpaulin
fn unreachable_hardware_path() {
    // This path requires actual GPU hardware to trigger
}

// For llvm-cov, use a more targeted approach:
// Simply accept that some paths need integration/hardware tests,
// not unit tests. Track them in a coverage exceptions list.

[dev-dependencies]proptest = "1"

use proptest::prelude::*;

proptest! {
    #[test]
    fn parse_never_panics(input in "\\PC*") {
        // proptest generates thousands of random strings
        // If parse_gpu_csv panics on any input, the test fails
        // and proptest minimizes the failing case for you.
        let _ = parse_gpu_csv(&input);
    }

    #[test]
    fn temperature_roundtrip(raw in 0u16..4096) {
        let temp = Temperature::from_raw(raw);
        let md = temp.millidegrees_c();
        // Property: millidegrees should always be derivable from raw
        assert_eq!(md, (raw as i32) * 625 / 10);
    }
}

[dev-dependencies]insta = { version = "1", features = ["json"] }

#[test]
fn test_der_report_format() {
    let report = generate_der_report(&test_results);
    // First run: creates a snapshot file. Subsequent runs: compares against it.
    // Run `cargo insta review` to accept changes interactively.
    insta::assert_json_snapshot!(report);
}

# Quick workspace coverage (proposed CI command)cargo llvm-cov --workspace \    --ignore-filename-regex 'tests?\.rs$' \    --fail-under-lines 75 \    --html# Per-crate coverage for targeted improvementfor crate in accel_diag event_log topology_lib network_diag compute_diag fan_diag; do    echo "=== $crate ==="    cargo llvm-cov --package "$crate" --json 2>/dev/null | \        jq -r '.data[0].totals | "Lines: \(.lines.percent | round)%  Branches: \(.branches.percent | round)%"'done