Ruby code coverage with SimpleCov

Add SimpleCov and the LCOV formatter

Add these gems to your test group and commit Gemfile.lock after running bundle install. The example uses RSpec; Minitest can use the same coverage setup in its test helper.

group :test do
  gem 'simplecov'
  gem 'simplecov-lcov'
end

Start coverage before loading application code

Put this at the top of spec/spec_helper.rb or test/test_helper.rb, before requiring your application. In Rails, ensure it runs before the environment is loaded. Adjust tracked source directories to match the repository.

require 'simplecov'
require 'simplecov-lcov'

SimpleCov::Formatter::LcovFormatter.config do |config|
  config.report_with_single_file = true
  config.single_report_path = 'coverage/lcov.info'
end
SimpleCov.formatter = SimpleCov::Formatter::LcovFormatter
SimpleCov.start do
  track_files '{app,lib}/**/*.rb'
  add_filter '/spec/'
  add_filter '/test/'
end

Run tests and upload the report

- uses: ruby/setup-ruby@v1
  with:
    bundler-cache: true
- run: bundle exec rspec
- uses: 9to5/9to5-coverage-action@v1
  with:
    token: ${{ secrets.COVERAGE_UPLOAD_TOKEN }}
    path: coverage/lcov.info

Add these steps after checkout in your GitHub Actions job and select the Ruby version used by the project. Run on the default branch and PRs. Confirm coverage/lcov.info exists and contains the intended app/lib files before uploading.

Avoid incomplete coverage

Starting SimpleCov after loading Rails or your library misses already-loaded code. Parallel test jobs require deliberate collation of their results before generating the final report; this single-process example does not merge CI shards. Keep source paths relative to the checkout.

SimpleCov documentation · LCOV formatter configuration