How to use Simplecov to find untested code in a Rails project with RSpec and Cucumber

Simplecov Show archive.org snapshot is a code coverage tool. This helps you to find out which parts of your application are not tested.

Integrating this in a rails project with rspec, cucumber and parallel_tests is easy.

1. Add it to your Gemfile and bundle

   Copygroup :test do
     gem 'simplecov', require: false
   end
   

2. Add a .simplecov file in your project root:

   CopySimpleCov.start 'rails' do
     # any custom configs like groups and filters can be here at a central place
     enable_coverage :branch # see https://github.com/colszowka/simplecov#branch-coverage-ruby--25
   end
   

   Note that we're using a predefined profile called rails which will group your models, controllers etc. in different tabs. You can also create your own profiles or use no profile at all.

   Optional: Enable "Branch Coverage" by adding enable_coverage :branch on Ruby 2.5+ projects to make Simplecov check if all possible branches of a condition have been hit.

3. Require in your features/support/env.rb for cucumber (important: require it before anything else, especially rails!):

   Copyrequire 'simplecov'
   SimpleCov.command_name 'features' + (ENV['TEST_ENV_NUMBER'] || '') # remove the TEST_ENV_NUMBER part if you don't use parallel_tests
   
   # ...
   

4. Require it in spec/spec_helper.rb for rspec (important: require it before anything else, especially rails!)

   Copyrequire 'simplecov'
   SimpleCov.command_name 'specs' + (ENV['TEST_ENV_NUMBER'] || '') # remove the TEST_ENV_NUMBER part if you don't use parallel_tests
   
   # ...
   

5. Consider disabling SimpleCov if you only run a fraction of your tests

6. Run your tests (rspec and cucumber)

7. At the end of the testrun you should see something like Coverage report generated for features, features2, features3, features4, specs, specs2, specs3, specs4 to /home/<user>/<my-project>/coverage.

8. (optional): add coverage/* to your project's .gitignore

9. Open the file with your browser: xdg-open coverage/index.html
   You should see a table like the one in the documentation Show archive.org snapshot .

10. Sort the table by "lines missed" to find the blind spots