Fixed most reported issues by SonarCloud.

game-loop/pom.xml

@@ -39,6 +39,12 @@
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
         </dependency>
+
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
     <build>
         <plugins>