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

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

lazy-loading/src/test/java/com/iluwatar/lazy/loading/HolderNaiveTest.java

@@ -31,7 +31,7 @@ import java.lang.reflect.Field;
  *
  * @author Jeroen Meulemeester
  */
-public class HolderNaiveTest extends AbstractHolderTest {
+class HolderNaiveTest extends AbstractHolderTest {
 
   private final HolderNaive holder = new HolderNaive();
 

lazy-loading/src/test/java/com/iluwatar/lazy/loading/HolderThreadSafeTest.java

@@ -31,7 +31,7 @@ import java.lang.reflect.Field;
  *
  * @author Jeroen Meulemeester
  */
-public class HolderThreadSafeTest extends AbstractHolderTest {
+class HolderThreadSafeTest extends AbstractHolderTest {
 
   private final HolderThreadSafe holder = new HolderThreadSafe();
 

lazy-loading/src/test/java/com/iluwatar/lazy/loading/Java8HolderTest.java

@@ -32,7 +32,7 @@ import java.util.function.Supplier;
  *
  * @author Jeroen Meulemeester
  */
-public class Java8HolderTest extends AbstractHolderTest {
+class Java8HolderTest extends AbstractHolderTest {
 
   private final Java8Holder holder = new Java8Holder();