Try to use JUnit instead of Gradle to run tests, mostly if you are running simple suites and you want to know the result faster

Initializing the Spring context is not cheap, do it only if it's necessary. The usage of annotations like @SpringBootTest is generally associated with Integration tests, and to avoid falling into the Ice Cream Cone anti-pattern, it is recommended to have more unit tests than integration tests, so don't put @SpringBootTest annotation everywhere

If you are using @SpringBootTest, try to reuse the context as much as you can, avoiding the anti-patterns I've mentioned before and doing some research if you see that it's not being reused and you are not using the annotations I said (to understand in which tests the Spring Context is being initialized, you should look in which test class the SPRING logo appears)

Use mocks only if it’s necessary, for example in case the context is difficult to reproduce. Don’t mock everything because you won’t end up testing anything at all.

https://blog.10pines.com/2022/05/20/a-quick-guide-to-spring-tests-optimization/