You don’t have to test them all end to end before merging a PR. You should have multiple stable pre prod environments for e2e testing. But if most changes fail e2e testing then your sdlc is broken before then and that should be fixed first. You need better designs and better collaboration and better local tests and code reviews.
> You don’t have to test them all end to end before merging a PR.
You have to test the changes you want to push. That's the whole basis of CI/CD. The question is at which stage are you ok with seeing your pipeline build.
If you accept that you can block your whole pipeline by merging a bad PR then that's ok.
In the meantime, it is customary to configure pipelines to run unit, integration tests, and sometimes even contract tests when creating a feature branch. Some platforms even provide high-level support for spinning up sandbox environment as part of their pipeline infrastructure.
