Unittest is the very first Python-based automated unit test framework that was designed to work with the Python standard library.

Supports the reuse of test suits and test organization.

It was inspired by JUnit and supports test automation including test collections, test independence, setup code for tests, etc.

It is also being called as PyUnit.

Unittest2 is a backport of additional new features added to the Unittest. 

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: