From the linked message, it seems Mr Fredric is most concerned that the test environments are broken. For my modules, that would be Test::More. Following the examples in the documentation, I rely on Test::More to set @INC appropriately. This appears to work, but I should enhance my tests to make sure that the version I expect to be tested is the one being tested.

He also said:

tests exposing runtime bugs are missing.

I assume this comment is targeted to the testing environment. However, I did try Corion's suggested test to see if any are affected by the change to @INC. Otherwise, none of my modules directly rely on @INC to load anything, so I don't know why I would have any tests for that. Configuration files are located by other means and not loaded with do, require nor use.