At first I started by looking for a good markdown test file to use for testing styling of HTML output generated from markdown. But all the tests were honestly kinda just bad? So I ended up using the GitHub markdown writing guide to figure out all the typical features of markdown and just created markdown_test.md on my own.
After a short break I checked Notion and realized that they don't actually return markdown OR EVEN HTML back from their API, but the markdown file was not to go to waste! Simply importing it into Notion proved super helpful as it exposed most of the features they typically support, after some slight fixing of links and adding of Notion-specific features it was perfect.
Then I got a Notion private integration up, after a bit of fiddling realized I had to invite the integration to have access to the page, then I was finally able to make requests to the page, you can see the requests and their responses in request.sh and responses folder representatively