TST: Adding unit tests

[Lucas-C]

I introduced the unit tests I originally developped in py-pdf/pypdf#2170

I also added a pytest -vv execution as part of the GitHub Actions pipeline

[Lucas-C]

@MartinThoma: I think you added a dependency to fpdf2 in https://github.com/py-pdf/pdfly/blob/main/pdfly/x2pdf.py#L6

But this dependency was not declared in https://github.com/py-pdf/pdfly/blob/main/pyproject.toml#L31

Which is why the unit tests are currently failing in the GitHub Actions pipeline:

Run pytest -vv
ImportError while loading conftest '/home/runner/work/pdfly/pdfly/tests/conftest.py'.
tests/conftest.py:6: in <module>
    from pdfly.cli import entry_point
pdfly/cli.py:19: in <module>
    import pdfly.x2pdf
pdfly/x2pdf.py:6: in <module>
    from fpdf import FPDF
E   ModuleNotFoundError: No module named 'fpdf'

If you agree, I can add fpdf2 to pdfly dependencies as part of this PR

[MartinThoma]

@Lucas-C Thank you for the many improvements 🙏

The PR looks awesome 🎉

One last question before we merge it: Where do the images come from?

[Lucas-C]

The images come from https://github.com/py-pdf/fpdf2/tree/master/test/image/image_types:

• https://github.com/py-pdf/fpdf2/blob/master/test/image/image_types/insert_images_insert_jpg.jpg
• https://github.com/py-pdf/fpdf2/blob/master/test/image/image_types/pythonknight.png

[MartinThoma]

Very nice! Thank you 🙏

[Lucas-C]

Thank you!

Now I'll have to fix those xfail-ing tests... 😅

We could also open issues with the hacktoberfest tag in order to invite contributors this month:
https://hacktoberfest.com/

[MartinThoma]

I like the idea of inviting new contributors :-) I would need to check what is required by us if we do that. I have no idea.

[Lucas-C]

I like the idea of inviting new contributors :-) I would need to check what is required by us if we do that. I have no idea.

I added a few issues with the hacktoberfest tag: hacktoberfest