After every deployment, instances of headless Chrome and Firefox are fired up. They visit the deployed app and run some basic checks, ensuring that the infrastructure was set up correctly, the deployment was successful, and the server runs as expected.
All this is powered by freely available open source tools. More info at my blog: https://vincenttunru.com/fearless-deployments/
Next to the app itself, it also deploys a Storybook, showcasing the app in the various states it can be in. This is perfect for quickly verifying the effect of styling changes, without having to run through countless scenarios in order to reproduce specific app states.