OpenCover vs SimpleCov

OpenCover has no write-up on Specifiction yet; its figures are above.

SimpleCov is a free, MIT-licensed tool for measuring Ruby code coverage with Ruby’s built-in Coverage library. It produces HTML and JSON reports and can merge results across test suites. Coverage types include line, branch, method, oneshot-line, and eval. Configuration supports filters, groups, profiles, and thresholds. Optional test tracking can show which RSpec examples or Minitest tests cover a line, while oneshot coverage can record code reached in production. The command line includes report viewing, test selection, patch coverage, history, status, and badge commands. A Rails profile can include ERB, Haml, and Slim templates in reports. SimpleCov can also calculate coverage for changed lines and apply a minimum threshold as a gate. The project says it is built in CI on Ruby 3.2+ and JRuby 10+; JRuby supports line coverage only. To track application files, SimpleCov must start before application code is required. The project directs code and bug reports to its issue tracker and discussion and announcements to its Google Groups mailing list.