Let's now adopt a practical approach. I will show you how to test a piece of code, and we will touch on the rest of the important concepts around unit testing, within the context of this example.
We want to write an export function that does the following: it takes a list of dictionaries, each of which represents a user. It creates a CSV file, puts a header in it, and then proceeds to add all the users who are deemed valid according to some rules. The export function takes also a filename, which will be the name for the CSV in output. And, finally, it takes an indication on whether to allow an existing file with the same name to be overwritten.
As for the users, they must abide by the following: each user has at least ...
