As part of our development process we routinely create unit tests that demonstrate the features of VistaDB. Each unit test demonstrates one aspect of using VistaDB - sometimes very narrow cases we want to prove and sometimes very broad cases (like connecting to a database). Internally we run these tests on every single build of VistaDB along with an additional several thousand tests that are provided to us by third parties for validation of our database.
For more information on unit testing and NUnit see Running VistaDB Unit Tests - What Is NUnit?.
The primary reason the unit tests are included in the VistaDB installation is to give you a set of examples to look at in code for how to perform a wide range of actions. While they don't necessarily represent best practices (indeed many tests are there to verify valid, but questionable, implementations) they can give you many ideas on how to get started or different patterns to try in your own code.
For a complete walkthrough see Running VistaDB Unit Tests -Running NUnit Tests.