refactor: remove code smell java:S5786 (#2159)

https://sonarcloud.io/organizations/iluwatar/rules?open=java%3AS5786&rule_key=java%3AS5786

twin/src/test/java/com/iluwatar/twin/BallItemTest.java

@@ -46,17 +46,17 @@ import org.slf4j.LoggerFactory;
  *
  * @author Jeroen Meulemeester
  */
-public class BallItemTest {
+class BallItemTest {
 
   private InMemoryAppender appender;
 
   @BeforeEach
-  public void setUp() {
+  void setUp() {
     appender = new InMemoryAppender();
   }
 
   @AfterEach
-  public void tearDown() {
+  void tearDown() {
     appender.stop();
   }
 
@@ -108,7 +108,7 @@ public class BallItemTest {
   /**
    * Logging Appender Implementation
    */
-  public class InMemoryAppender extends AppenderBase<ILoggingEvent> {
+  class InMemoryAppender extends AppenderBase<ILoggingEvent> {
     private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender() {