The only line of code in this recipe creates a file called .travis.yml in the root of your package directory. This file works as a hook on GitHub so that, once the repository is updated, the Travis.CI server will carry out a new build of the virtual server and package and run the tests, then email you the results at the address associated with your GitHub account. Although it is only one line, this is probably one of the most impactful single lines in this whole book! The .travis.yml file carries configuration options for the Travis build and much can be added to customize the output. One common addition to that file is as follows:

warnings_are_errors: false

This will tell Travis that warnings from R code are not to be counted as errors and won't make the build fail. 

A build can take time; expect even simple code to take 15 minutes. More complicated projects will take longer.