Before running test using CircleCI go for https://circleci.com/ to Sign Up.
After Log In, all existed projects for some Github repo will be automatically available for setting up.
Create .circleci/config.yml in the root directory. Here are the link with a detailed manual how to write config.yml.
This document describes common methods for running and debugging browser testing in your CircleCI config:
The Latest Circleci-dockerfiles:
- https://circleci.com/docs/2.0/docker-image-tags.json
- https://github.com/CircleCI-Public/circleci-dockerfiles/tree/master/python/images
Each commit for the project triggers running CircleCI job.