Whilst I won’t be showing code in this, there is a companion sample database project. This is on GitHub and each key stage is shown by a branch of work. This means you can jump in at most stages and work from there. If you need some git advice, check out my quick git in 5 presentation.
The core DB is a super hero themed database.
Database unit testing involves a lot of compromises (because most of what we care about as database professionals tends to be integration tests rather than unit tests), but having imperfect tests generally beats having no tests, so check this out.