This is a sample application with the required configuration to get JavaScript code coverage for JavaScript, TypeScript and React, and also Ruby code coverage, using SimpleCov, Capybara and Istanbul.
Ruby version: 2.6.5
This app contains the setup to run both RSpec and MiniTest test suits and get the code coverage.
If you want to use RSpec, you can run COVERAGE=true rails spec
If you want to use MiniTest, you can run COVERAGE=true rails test:system or COVERAGE=true rails test:all