Continuous Integration (CI) services can run your tests in several environments: various operating systems, browsers or Node versions. It would be complicated to set up on your local machine. Usually, CI checks every commit to your master or development branch, as well as on each pull request; CI will prevent merge or deploy if there are any errors. It’s common practice to run long processes on CI: integration tests, code coverage reports, etc. Some projects even publish new releases automatically on CI.