Added hex converter unit tests

src/test/java/Main/UtilsTest.java

@@ -0,0 +1,15 @@
+package Main;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class UtilsTest {
+
+    @Test
+    void stringToHexHexToStringTest(){
+        String text = "6f1a";
+        byte[] bytes = Utils.stringToBytes(text);
+        String result = Utils.bytesToHex(bytes);
+        assertEquals(text, result);
+    }
+}