The comment says the same thing as the code, but is less thorough. I'd rather the comment told me something I can't tell from the code, such as exactly what is supposed to be dubious about the file used.

I would move the declaration of `expectedLocales` up here (it is part of the given scenario for this test), and name it to clarify why that is expected (i.e. that these are the locales for which there are tuvs in the file that was used). Source locale in the file could similarly be extracted to an explanatory variable in this section.