[devit]

I don't mean testing against the production instance, but rather against an instance configured like the production instance, except for being scaled/sized appropriately for the testing data and workload instead of the production one.

It's also possible to test against live production instances and data itself (mostly useful for performance optimization work and testing), although that's more of an ad-hoc process and some kinds of tests are not possible because the actual data there is arbitrary. Also, those tests, if not used for development, might be better expressed as self-checks done on system start and monitoring systems.