As long as the bulk of the unit tests run and report correctly everything is, of course, fine. I was under the wrong belief that unit testing aborted very early on if the C locale was defined. Of course having some tests refuse to run on the grounds that the system is not configured to support the tests is common in all testing and i apologise.
The problem is that pdf_text_init (the function that initializes the text module) is not able to work when the user locale is C or POSIX, so _any_ test involving the text module will fail if you have such locales activated in your environment.
