Let's start our unit testing journey with the data models we wrote for the Notes application. Because this is unit testing, the models should be tested separately from the rest of the Notes application.

In the case of most of the Notes models, isolating their dependencies implies creating a mock database. Are you going to test the data model or the underlying database? Testing a data model and not mocking out the database means that to run the test, one must first launch the database, making that a dependency of running the test. On the other hand, avoiding the overhead of launching a database engine means that you will have to create a fake Sequelize implementation. That does not look like a productive use of our time. One can argue that testing a data model is really about testing the interaction between your code and the database, that mocking out the database means not testing that interaction, and therefore we should test our code against the database engine used in production...