When I joined at Thumbtack, back in late 2015, we had continuous delivery infrastructure for monolith builds. As more engineers joined, we noticed that a significant amount of time went to deploying the latest build. Moreover, there was a trend of having bigger deploys (so call train deploys) and rollbacks tend to be harder. It was a clear indicator we needed to invest into the deployment pipeline.
At Thumbtack, we use Gerrit for code review. As soon as a Code Review is submitted, Jenkins starts the build process. The source code is fetched from Gerrit’s Git repository and series of unit tests are executed.