A CI or other _testing system_ that would like to discover, stage and invoke tests for a _test subject_.Examples: https://jenkins.io/[Jenkins], https://taskotron.fedoraproject.org/[Taskotron], https://docs.openstack.org/infra/zuul/[ZUUL], https://ci.centos.org/[CentOS CI], https://github.com/projectatomic/papr[Papr], https://travis-ci.org/[Travis], https://semaphoreci.com/[Semaphore], https://developers.openshift.com/managing-your-applications/continuous-integration.html[Openshift CI/CD], https://wiki.ubuntu.com/ProposedMigration/AutopkgtestInfrastructure[Ubuntu CI]...