The tests are organised into related topics and build up concepts over time through examples in a similar way to The Little Schema book and From Nand to Tetris.

You can read more about the project at https://technicaldeft.com/posts/rgsql-a-test-suite-for-datab...

I have also written an accompanying book to guide people through the project and learn how real world databases and query engines work: https://technicaldeft.com/build-a-database-server