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Code coverage of Ruby on Rails application with simplecov

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Post summary: How to measure code coverage of Ruby on Rails application with simplecov.

This is going to be a pretty short post. In general, it is very easy to measure code coverage on Ruby on Rails applications with a gem called simplecov.

Add coverage to Gemfile


gem 'simplecov', require: false

By using the require: false, Gem gets installed but it is not included when bundler is called. In order to use the Gem you manually have to call require ‘simplecov’.

Start code coverage

Starting the code coverage should be the first thing that the application is doing. So it can be invoked in config/boot.rb file. Add the following lines:

if ENV['ENABLE_CODE_COVERAGE']
    require 'simplecov'
    SimpleCov.start 'rails'
end

Do the testing

A small part in the current post, huge part in the actual effort. Run all the tests that you have, manual, automated, etc.

Gather code coverage

There are basically two ways to get the code coverage: shutdown the application or somehow call SimpleCov.result.format!. Not much to say on the first one. In many cases, it is more convenient to keep the application running, but only the coverage report. For the latter, you may have some controller which is available on for non-production environments, which you can hit with an HTTP call and it executed the code. The code coverage report is located in a folder called coverage in the root application folder.

Conclusion

It is pretty easy to measure code coverage on Ruby on Rails applications with the simplecov Gem.

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