Test coverage¶

Test coverage support is provided by third-party tools that wrap around nextest.

llvm-cov¶

cargo-llvm-cov supports nextest. To generate llvm-cov data with nextest, run:

cargo install cargo-llvm-cov
cargo llvm-cov nextest

Using llvm-cov in GitHub Actions¶

Install Rust with the llvm-tools-preview component, nextest, and llvm-cov in GitHub Actions. Then, run cargo llvm-cov nextest.

- uses: dtolnay/rust-toolchain@stable
  with:
    components: llvm-tools-preview
- uses: taiki-e/install-action@cargo-llvm-cov
- uses: taiki-e/install-action@nextest

- name: Collect coverage data
  run: cargo llvm-cov nextest

Collecting coverage data from doctests¶

Nextest doesn't currently support doctests, so coverage data from nextest must be merged with doctest data.

Here's an example GitHub Actions configuration:

# Nightly Rust is required for cargo llvm-cov --doc.
- uses: dtolnay/rust-toolchain@nightly
  with:
    components: llvm-tools-preview
- uses: taiki-e/install-action@cargo-llvm-cov
- uses: taiki-e/install-action@nextest

- name: Collect coverage data (including doctests)
  run: |
    cargo llvm-cov --no-report nextest
    cargo llvm-cov --no-report --doc
    cargo llvm-cov report --doctests --lcov --output-path lcov.info

Reporting to an external coverage service¶

External services like Codecov.io can be used to collect and display coverage data. Codecov is free for open source projects, and supports lcov.info files.

After generating an lcov.info file, upload it to Codecov with:

- name: Upload coverage data to codecov
  uses: codecov/codecov-action@v3
  with:
    files: lcov.info

Example¶

Nextest itself uses the above mechanisms to collect coverage for its project. The config is located in .github/workflows/coverage.yml.

Integrating nextest into coverage tools¶

Most coverage tools work by setting a few environment variables such as RUSTFLAGS or RUSTC_WRAPPER. Nextest runs Cargo for the build, which will read those environment variables as usual. This means that it should generally be quite straightforward to integrate nextest into other coverage tools.

If you've integrated nextest into a coverage tool, feel free to submit a pull request with documentation.