Tests write files to disk

[pdiercks]

I noticed that some of the tests or at least test_thermo_mechanical_cube
write xdmf files to disk for no apparent reason.

If there is a reason, but the files are not compared to some reference data afterwards, I would suggest that these could simply be temporary files. Something like

import tempfile
import pathlib

tf = tempfile.NamedTemporaryFile(suffix=".xmdf")
pv_name = pathlib.Path(tf.name).stem  # it seems class below does not want suffix?

# ... lots of code ...

problem_elastic = LinearElasticity(experiment, parameters, pv_name=f"{pv_name}_{dim}", pv_path="")
problem_elastic.solve()
problem_elastic.pv_plot()

tf.close()  # temporary file is deleted when closed