[m-rev.] for post-commit review: extend filename generation test infrastructure

[Zoltan Somogyi]

On 2023-06-04 18:20 +02:00 CEST, "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> For review by anyone.

The attached diff does not contain the sorting of the extensions,
but the commit does.

Zoltan.