Setting up parallelism
This two-minute video shows you everything you need to do to turn parallelism on for your project. (This video assumes you already have a green build without parallelism. Check out our getting started guide if you haven’t setup your project yet.)
In summary, just go to the project settings page by clicking on the gear icon in the top-right, then click “Parallelism”. Then simply choose the number of parallel containers you want to use on each build.
CircleCI can automatically split your tests across multiple containers for many test runners, including RSpec, Cucumber, minitest, Django, Nose, and more. For the most popular frameworks, we support optimizing the distribution based on how long each test takes to run - see our doc on test metadata for more information on using this feature. Otherwise we divide files or test classes evenly across containers, which provides a good balance in most cases.
However, if our inferred parallel test commands don’t work, or if you want to do custom test splitting, see our doc on manually setting up parallelism.