The quality of the test environment isn’t guaranteed though. I ran a production system that had a shell of a “test” environment with no data from prod. I repeatedly told the vendor testing in their “test” environment was worthless because without the prod data I had no real way to recreate so many of the situations that naturally came up for my users in the production software. The vendor refused to correct the problem, so I told them - with all the relevant managers present - to stop asking me to waste my time testing new releases when doing so was effectively useless.