We have extension_foo_upgrade_downgrade.js and extension_foo_upgrade_downgrade_auth.js, where the former runs solely in environments where auth is disabled and the latter runs solely in environments where auth is enabled.

I thought I was being clever by having the auth version import helper functions from the non-auth file to avoid redundancy. BUT - it turns out that when importing a function from a file, it has to parse and evaluate the entire file. That means that running the auth version also runs the non-auth version, in the wrong context (auth enabled). The fix is simply moving the re-used functions to their own file that is imported to both the executable test files. This will resolve BF-39277.