[WIP] ENH: Add unittest suite with pytest (#3)

[jblemoine]

Description

Unittest for clean, convert and write modules.
I added a series of unittest with pytest. Work still in progress since I don't know how to assess a good yaml format.

Fixes # (issue)

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation if any
• My changes generate no new warnings
• I have added tests that prove my fix is effective, if unittests are enabled
• New and existing unit tests pass locally with my changes, if any

[LaRiffle]

Nice start!
I responded to Issue #3 :)