Microsoft doesn't. They do automated testing. So if a software company is doing that, I guess at best Sammy does the same.
Edit: I mean, there should be a manual QC team.
I doubt that happens. Automated tests are 100% reliable for devices with specific applications. For smartphones and PC, we are the perfect samples.
MS does this on various benches with various PC configurations. On top of that, they have various preview branches and they also test using those "I need to update ASAP" people.
In the case of Samsung, there are limited configurations. Also, I do not think you can create multiple scenarios in a lab as there are many variables (geography, network config etc). Many things are user-dependent and it's hard to cover everything that a user might face. They probably have an insider beta testing group for testing updates. Still, it's hard to cover every single variable. If they have an insider testing group then they should try to cover as much as possible. Maybe release a few devices so they do not have to face time constraints while covering everything.
*I work in a similar field. All of this is just an educated guess. They may have an extensive testing program or maybe they don't have anything at all.