JaCoCo is one the most used tools for generating coverage reports for JUnit tests. One of the reasons for it being so used is it's seamless integration with tools like Jenkins, SonarQube, Maven and Gradle.
With Gradle, very little comes out of the box and a lot of the filtering and configuration you need to do on your own. That can be confusing at first especially as a beginner and even more so if you are accustomed to Maven.
Drift to low performance is one such trap when by allowing standards to be influenced by past performance, especially when past performance is perceived as bad, sets up a reinforcing feedback loop of eroding goals that set a system drifting toward low performance.