Emily Bache's short example of preparing "Approval Tests" for refactoring Python code is very good. Not only for the approach, but also for how advanced IDEs like PyCharm greatly support developers common editing and refactoring needs.
Reaction: Arjan Codes wrote tests the HARD way - My way is BETTER - YouTube
I do like computational notebooks, but find them cumbersome to work within. If like me, you've been looking for a notebook-like experience, coding in python, editing using your preferred editor, auto reloading, primarily local, deployable to a small audience, etc then Kris Jenkins's talk Building Data Visualisations in Python in Minutes about Streamlit will be of interest.