[WIP] CI move to pytest

[glemaitre]

Move the test inside a testing framework.

[glemaitre]

It seems strange that the current test was not passing in python 3. At least the reading part seems consistent. I would assume that this is the writing which could be different. I did not check which part of the code is not covered for the moment.

[glemaitre]

For the moment the line which are not covered are linked to plot and and output.
Otherwise there is the Shimadzu format which seems to not be covered. I assume that there is not file to test this part of the code.