My Micropub endpoint has a fair bit of unit testing inside the Java project ( https://gitlab.com/jamietanna/www-api/tree/develop/www-api-web/micropub ) for common flows, but I've also found a tonne of implementation issues by integrating with real Micropub clients.
Some of it is an issue on a Micropub client, but most of it is something I've missed or assumed incorrectly.
I'm thinking to create a stubbed version ( https://gitlab.com/jamietanna/www-api/issues/26 ) that I can then use with https://micropub.rocks to ensure compliance.
Some of it is also a case of reading through the Micropub spec!