This is a Gradle project, currently using Java 14, AssertJ for assertions, and JUnit 5.

IntelliJ IDEA note:

In IDEA, if you receive an error similar to:

Could not target platform: 'Java 14' using tool chain: 'JDK 7 (1.8)'

...navigate to the Properties (Settings) dialog, search for Gradle, and change the Gradle JVM appropriately.