add check if all notebooks have md with badges, md with description and Colab header

[AgnieszkaZaba]

I added three tests proposed by @slayoo in #8. Changed order of cells in notebooks as:

1. markdown with badges
2. markdown with description
3. Colab header

In test_third_cell_contains_colab_header I set cell index as 2.

[slayoo]

Thank you @AgnieszkaZaba !
(closed and reopened the PR to trigger CI tests which were auto-disabled by GitHub due to project inactivity)

[AgnieszkaZaba]

@slayoo Should I add definitions of badge functions to test_notebooks.py or is it better to use utils?

[AgnieszkaZaba]

I added badge functions to test_notebooks.py for now.

There is a problem with empty.ipynb because it does not have proper structure. Should we change it or maybe exclude from those tests?

[slayoo]

I added badge functions to test_notebooks.py for now.

👍

There is a problem with empty.ipynb because it does not have proper structure. Should we change it or maybe exclude from those tests?

Let's either rename it to template.ipynb and add there all the features that are tested, or add a separate template.ipynb file.

BTW, we maintain a set of "hints" for Python development here: https://github.com/open-atmos/python-dev-hints/wiki