While working on the last PR I've got in the situation when kokoro checks passed (green), but after some time their status became red (because some parallelized tests failed - some can take more than 20 min.). This can cause problems with "automerge" (bot that runs checks and merges PR automatically, if they are green). Automerge is used in the original Spanner repo, which means this API will be using it too. And, after all, it's inconvenient when checks are green, but can become red in future (~35 min.).