A Travis build will either pass or fail. If the build fails, it will be accompanied by a red cross:

By default, Travis will also send an email notifying us of the result of the build and tests:

Travis also integrates with GitHub's Commit Status API (developer.github.com/v3/repos/statuses/), which allows third parties to attach a status to commits. Here, Travis is attaching the failure state to the comment, which shows up as a red cross indicator next to the commit time:

But, most importantly, each run also saves the history of the logs, so in cases of error, the developers are able to pinpoint the issue and fix it quickly: