Fix Gradle test dependencies loading

[rob93c]

This pull request aims to fix the following warning Gradle shows when launching unit tests:

The automatic loading of test framework implementation dependencies has been deprecated. This is scheduled to be removed in Gradle 9.0. Declare the desired test framework directly on the test suite or explicitly declare the test framework implementation dependencies on the test's runtime classpath. Consult the upgrading guide for further information: https://docs.gradle.org/8.4/userguide/upgrading_version_8.html#test_framework_implementation_dependencies

In addition to this, the code has been cleaned up in some classes.

[MartelliEnrico]

LGTM