It's a lot easier to do in an application that's easy to boot up locally. A lot of software in web-startup world grows out of that stage once the k8s/distributed architecture earworm burrows in.

It can be an automation thing. With tools like (Github) Codespaces there are places today that have the ability to deploy every random PR branches and do PRs in a full code editor backed with a running deployment that you can browse. Admittedly, that's a lot easier to do when what you are deploying is web-based and automating spinning up new URLs (even just proxy forwarded localhost URLs in the case of Codespaces) is easy and things are a lot harder to automate with for instance mobile apps.

If there are engineers on the team wo assign PR for review that aren’t tested by themselves or don’t contain automated software tests (if the project has such standard) it’s time for the manager to have a 1on1 discussion about professional standards. Sometimes juniors aren’t aware of these shortcomings or are coming from a shop with bad development practices. They just need sometimes to learn professional practices and there is nothing lost.

If you can get people to test in review, I don't see why you couldn't get them to test before review. If you can't get your developers to test appropriately, then you've hired bad developers.