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

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

specification/src/test/java/com/iluwatar/specification/selector/MassSelectorTest.java

@@ -33,7 +33,7 @@ import com.iluwatar.specification.creature.Creature;
 import com.iluwatar.specification.property.Mass;
 import org.junit.jupiter.api.Test;
 
-public class MassSelectorTest {
+class MassSelectorTest {
 
   /**
    * Verify if the mass selector gives the correct results.

specification/src/test/java/com/iluwatar/specification/selector/MovementSelectorTest.java

@@ -38,7 +38,7 @@ import org.junit.jupiter.api.Test;
  *
  * @author Jeroen Meulemeester
  */
-public class MovementSelectorTest {
+class MovementSelectorTest {
 
   /**
    * Verify if the movement selector gives the correct results.

specification/src/test/java/com/iluwatar/specification/selector/SizeSelectorTest.java

@@ -38,7 +38,7 @@ import org.junit.jupiter.api.Test;
  *
  * @author Jeroen Meulemeester
  */
-public class SizeSelectorTest {
+class SizeSelectorTest {
 
   /**
    * Verify if the size selector gives the correct results