What Design Patterns are more suitable for script automation tests?

I have building a series of scripts to do data preprocessing, calculating and imputation on a database system, so basically, an ETL job using python. However, this specific script is getting bigger and bigger at every new request from business analysts, and I was thinking in transforming it into a more 'formal' project. So I am looking for design patterns suitable to work with automation tasks in Python, is there any? Also, I intend to start doing TDD on top of it to diminish my debugging time.

I might be overthinking and the code with modules and functions can do it, but since I am out of my field of knowledge, I don't even know what to search for.