If you have a project of any complexity that is using Travis CI for testing, you’ve inevitably run into an issue where you make a minor change – maybe even just to a markdown file – and the tests that were passing before completely bomb. If this hasn’t happened to you, just wait, it will! This typically happens because some dependency, such as a newer rubygem you depend on indirectly, is no longer compatible with your test environment. As an example, I updated my .travis.yml in a puppet module project, opened PR16, and suddenly all the previously-green tests went red. The error NoMethodError: undefined method 'last_comment' for #<Rake::Application:0x000000015849f8> was observed because the dependent gem rake was updated from v11 to v12, conflicting with the pinned version of rspec. Until this problem is fixed, every PR, no matter how simple or complex, is going to fail its test.

This puts a lot of burden on both the person submitting the PR, who just wants their simple change to be approved, and the project maintainer, who wants their build status to work. Neither is satisfied until the problem is tracked down and remediated, often in a separate PR. By that time, the contributor may not have the interest to update their PR and the maintainer has to decide if they want to fix it up or discard it. No-one is happy. All because some upstream dependency changed and we weren’t aware of it until the moment a PR was submitted, even though it may have happened days or months ago.

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