Description
https://spring.io/guides/gs/testing-web/
The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there is not a single line of XML? There is no web.xml file, either. This web application is 100% pure Java and you did not have to deal with configuring any plumbing or infrastructure. Spring Boot handles all of that for you.
Logging output is displayed. The service should be up and running within a few seconds.
This feels like the description of running the application is missing. Logging output of what is displayed?
There's a similar text on https://spring.io/guides/gs/rest-service/, just between those two paragraphs there is a description of how to run the application.
I guess one needs to do the same (for example gradlew bootRun), and only then run the tests (gradlew test). I would say this is pretty important part that is omitted right now.