Added a unit test for Characters

test/util/CharactersTester.java

@@ -0,0 +1,20 @@
+package util;
+
+import static org.junit.Assert.assertTrue;
+
+import java.lang.reflect.*;
+
+import org.junit.Test;
+
+public class CharactersTester {
+
+    @Test
+    public void testConstructorIsPrivate() throws Exception {
+        Constructor<Characters> constructor = Characters.class.getDeclaredConstructor();
+
+        assertTrue(Modifier.isPrivate(constructor.getModifiers()));
+        constructor.setAccessible(true);
+        constructor.newInstance();
+    }
+
+}