RSpec for Rails: Advanced Techniques #1 - Parallelization

What is Test Parallelization

Test parallelization is the process of running tests simultaneously on multiple threads or processes, instead of one after the other. This can significantly reduce the time it takes to run a full test suite. By parallelizing your tests, you can also catch issues faster, allowing you to focus on writing new features.

Implementing Test Parallelization with RSpec

RSpec provides a number of ways to run tests in parallel. One of the easiest ways to get started with test parallelization is by using the parallel_tests gem. The parallel_tests provides a rake task that splits your test suite into multiple processes, allowing you to take advantage of multi-core CPUs.

Here’s how to install and use parallel_tests:

1. Add parallel_tests gem to your Gemfile:

    group :test do
      gem 'parallel-tests'
    end
   

2. Run bundle install to install the gem.

3. Update your config/database.yml to consider the number of the test the database name.

    test:
      database: application_test<%= ENV['TEST_ENV_NUMBER'] %> 
   

   Change application to your project name or any other name you use for your database. ENV['TEST_ENV_NUMBER'] will be the number of the instance being tested. For now we’ll just consider that the parallel_tests gem will handle this instances for us.

4. Create additional databases by running the rake parallel:create task.

    rake parallel:create
   

5. Run your tests in parallel using rake parallel:spec task.

    rake parallel:spec
   

It’s that simple! parallel_tests will automatically split your test suite into multiple processes, allowing you to take advantage of multi-core CPUs.

You may want check the parallel_tests GitHub page to get more insights and learn more advanced settings and tasks to run. In this article we went only though the basics concepts.

Conclusion

In this article, we discussed how to improve your test performance through test parallelization in Rails using the parallel_tests gem. By running your tests in parallel, you can reduce the time it takes to run a full test suite, catch issues faster, and focus on writing new features.

Stay tuned for the next article in this series, where we will discuss how to leverage shared examples and context for DRY tests.