Loading test data into a PostgreSQL database

Hi,

I'm currently working on a project using PostgreSQL 13 and using an extension with CREATE EXTENSION to create the
database.However, if I want to make certain changes to the database, I have to drop the extension and then re-create it
(Idon't want to update the version number for the initial release). So, what is the normal way of creating some test
datato put in the database because obviously, when you do DROP EXTENSION, it deletes everything? 

Can I make a CSV file and import it into the database? Or do I have to write some custom SQL to handle that aspect? Or
isthere an easier method I should be using? Or could I add some test data to the extension itself? 

Simon.