Refactor tests with fixtures to have better file creation/deletion management

[Karolina-Bogacka]

Use FixtureSpec to make a set of repeatable fixtures for easy setup/teardown of unit test (creation and deletion of files of a given format etc). It should be possible to combine multiple fixtures in a given test if needed. To combat any parallelization issues, the file names should depend on the full name of a given unit test and be therefore unique within the whole testset.

[Ostrzyciel]

Please elaborate a tiny bit on what to do in the task description. Thanks!

[Karolina-Bogacka]

ok, done!