How can I test a procedural python script properly

I'm pretty new to Python. However, I am writing a script that loads some data from a file and generates another file. My script has several functions and it also needs two user inputs (paths) to work.

Now, I am wondering, if there is a way to test each function individually. Since there are no classes, I don't think I can do it with Unit tests, do I?

What is the common way to test a script, if I don't want to run the whole script all the time? Someone else has to maintain the script later. Therefore, something similar to unit tests would be awesome.

Thanks for your inputs!