I think they have to be long lived else they cannot make sense for performant testing. ie they are created as DB objects, using DDL, in the same way tables, views, functions etc are made.
They can certainly be created at test run time but that would slow things down a lot - you would essentially be creating a ton of objects every time you run the test which means having a setup to test if they exist or not, take them down if they do or fix them if they don't match spec ( e.g. column and data type changes etc etc )
The more I think about this, the more complicated I realize it would be to manage this dynamically:
You essentially have to build a test harness enviroment that figures out your testing elements dynamically from your data environment (with some kind of parameterization engine and data set to tell it what to look for so as to "make functors and run them" (e.g. all PKs of FKs or all columns starting with a certain prefix or all columns of a certain data type etc etc), gets the most up to date definitions of those elements from system tables and uses that data to create or update or drop functor objects ... wow, ok, this is getting complicated, I am going to stop now before I see the void.
They can certainly be created at test run time but that would slow things down a lot - you would essentially be creating a ton of objects every time you run the test which means having a setup to test if they exist or not, take them down if they do or fix them if they don't match spec ( e.g. column and data type changes etc etc )
The more I think about this, the more complicated I realize it would be to manage this dynamically:
You essentially have to build a test harness enviroment that figures out your testing elements dynamically from your data environment (with some kind of parameterization engine and data set to tell it what to look for so as to "make functors and run them" (e.g. all PKs of FKs or all columns starting with a certain prefix or all columns of a certain data type etc etc), gets the most up to date definitions of those elements from system tables and uses that data to create or update or drop functor objects ... wow, ok, this is getting complicated, I am going to stop now before I see the void.