In develop, master, and any other branch configured in circle.yml, the Cypress binary and npm package are built and uploaded to cdn.cypress.io. Then, tests are run, using a variety of real-world example repositories.
Two main strategies are used to spawn these test projects:
test-binary-against-repojobs- Remote CI
A number of CI jobs in circle.yml clone test projects and run tests as part of cypress-io/cypress's CI pipeline.
You can find a list of test projects that do this by searching for usage of the test-binary-against-repo step.
Similarly to "Remote CI" test projects, Local CI test projects will attempt to check out a branch that is named after the next version (X.Y.Z) if one exists in the test project git repo.
One advantage to local CI is that it does not require creating commits to another repo.
System tests in /system-tests/test-binary are run against the built Cypress App in CI. For more details, see the README.