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Render has some great features like making a new sub domain for when a PR is opened so you can test it as a fully working API before you merge

I believe Netlify introduced this feature. It is now ubiquitous (as alexgrover said).

That’s supported on most PAAS these days, including Heroku.

On their free tiers though?

Well, no longer free on Heroku, but it was

did not know heroku had that.