Unit testing involves testing individual units or components of your application in isolation. In Spring Boot, you can use JUnit or any other testing framework to write unit tests for your application. You can use mock objects to simulate dependencies, so that you can test your code without relying on external systems. Unit tests can help you to catch bugs early in the development process and ensure that your code is functioning as expected.

Here’s an example of a simple unit test for a Spring Boot application using JUnit and Mockito:

Suppose we have a UserService class that depends on a UserRepository interface: 

The model tests are omitted here because they are essentially the same as in the impure section. In contrast to the tests on the impure service, we will now write unit tests for our routes.

This means that we will be able to test our routing logic without spinning up a database.

Test repository

To be able to test our routes, we will have to implement a TestRepository first, which we will use instead of the concrete implementation that is wired to a database.

Base class for unit tests

Testing Product fromDatabase

Testing a JSON codec

Testing decoding garbage input

Testing invalid input values

Testing valid input

Testing included fields

Decoding encoded JSON

More tests

Testing Translation fromUnsafe

Base class for unit tests

To avoid repeating the construction of our unit test classes, we will implement a base class for tests, which is quite simple.