The Spring Boot test starter package is added to pom.xml by Spring Initializr when we created our project. That is added automatically without any selection in the Spring Initializr page:

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>

The Spring Boot test starter provides lot of handy libraries for testing, such as JUnit, Mockito, AssertJ, and more. If you look, your project structure already has its own package created for test classes:

By default, Spring Boot uses an in-memory database for testing. We are now using MariaDB, but H2 can also be used for testing by adding the following dependency to the pom.xml file. The scope defines that the H2 database will be used only for running tests; otherwise, the application will use the MariaDB database:

    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>test</scope>
    </dependency> 

If you also want to use the default database for testing, you can use the @AutoConfigureTestDatabase annotation.