Fixed most reported issues by SonarCloud.

subclass-sandbox/pom.xml

@@ -44,6 +44,11 @@
             <groupId>com.github.stefanbirkner</groupId>
             <artifactId>system-rules</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>