Fix test classes without tests or assertions

[thboileau]

cf Sonar report:

• https://sonarcloud.io/project/issues?open=AZzOKEgFDgifRzo4K57r&id=restlet_restlet-framework-java
• https://sonarcloud.io/project/issues?open=AZzOKEjMDgifRzo4K59Y&id=restlet_restlet-framework-java
• https://sonarcloud.io/project/issues?open=AZzOKEXRDgifRzo4K51f&id=restlet_restlet-framework-java
• https://sonarcloud.io/project/issues?open=AZzOKER2DgifRzo4K5xD&id=restlet_restlet-framework-java
• https://sonarcloud.io/project/issues?impactSeverities=BLOCKER&issueStatuses=OPEN%2CCONFIRMED&id=restlet_restlet-framework-java&open=AZzOKEVZDgifRzo4K50N