Fix tests

Problem/Motivation

It looks like tempnam() triggers a deprecation notice that breaks the test because it thinks the file system is not writable, likely because kernel tests actually use a virtual file system.

Proposed resolution

The call actually happens twice, for whateve reason. We can just remove that. I think we could actually easily drop thet whole tempnam() business completely as this is not just a folder that is unique for each test run, it is a *virtual* folder. That said, maybe it actually doesn't work there, so the second line was added.

I have no idea why the deprecation message is only triggered for 8.x-2.x.

Remaining tasks

User interface changes

API changes

Data model changes