add test and method

jpos/src/main/java/org/jpos/iso/ISOUtil.java

@@ -32,6 +32,10 @@
 import java.util.StringTokenizer;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
+import java.util.regex.Pattern;
+import java.math.BigInteger;
+import java.util.regex.Pattern;
+import java.util.regex.Matcher;
 
 /**
  * various functions needed to pack/unpack ISO-8583 fields
@@ -177,7 +181,19 @@ public static String trim (String s) {
     public static String zeropad(String s, int len) throws ISOException {
         return padleft(s, len, '0');
     }
-
+
+    public static boolean isHexadecimal(byte[] bytes) {
+        for (byte b : bytes) {
+            int unsignedByte = b & 0xFF;
+            if (!((unsignedByte >= 0x30 && unsignedByte <= 0x39) ||  // Dígitos 0-9
+                  (unsignedByte >= 0x41 && unsignedByte <= 0x46) ||  // Letras A-F
+                  (unsignedByte >= 0x61 && unsignedByte <= 0x66))) {  // Letras a-f
+                return false;
+            }
+        }
+        return true;
+    }
+
     /**
      * zeropads a long without throwing an ISOException (performs modulus operation)
      *
@@ -680,8 +696,26 @@ public static byte[] hex2byte (byte[] b, int offset, int len) {
      * @return byte array
      */
     public static byte[] hex2byte (String s) {
-        return hex2byte (s, CHARSET);
+
+        if (s.isEmpty() || s.length() % 2 != 0) //verificar si el string es vacio
+        {
+            throw new IllegalArgumentException("The string is empty or null, invalid hexadecimal");
+        }
+        // Verificar si cada carácter es un dígito hexadecimal válido
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i); 
+            if (!isDigitHexadecimal(c)) {
+                throw new IllegalArgumentException("The string is not hexadecimal");
+            }
+        }
+        return hex2byte(s, CHARSET);
+
+    }
+
+    public static boolean isDigitHexadecimal(char c) {
+        return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f');
     }
+
     /**
      * Converts a hex string into a byte array
      * @param s source string (with Hex representation)

jpos/src/test/java/org/jpos/iso/ISOUtilTest.java

@@ -34,6 +34,7 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
+import static org.junit.Assert.assertArrayEquals;
 
 import java.math.BigDecimal;
 import java.math.MathContext;
@@ -43,13 +44,36 @@
 import java.util.Calendar;
 import java.util.GregorianCalendar;
 import java.util.TimeZone;
+import java.util.regex.Pattern;
 
-import org.junit.jupiter.api.Assertions;
+import org.fest.assertions.Assert;
 import org.junit.jupiter.api.Test;
+import org.junit.Assert;
+import java.util.Arrays;
 
 public class ISOUtilTest {
     final String lineSep = System.getProperty("line.separator");
 
+
+
+    @Test
+    public void testHex2byte_ValidInput() {
+        byte[] result = ISOUtil.hex2byte("1A2B3C");
+        byte [] expected = {0x1A, 0x2B, 0x3C}; 
+        assertArrayEquals(expected, result);
+    }
+
+    @Test
+    public void testHex2byte_InvalidInput_ThrowsExceptionWithMessage() {
+
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> {
+            ISOUtil.hex2byte("1111");
+        }, "Not hex");
+
+        assertEquals("Not hex", exception.getMessage());
+    }
+
+
     @Test
     public void testAsciiToEbcdic() throws Throwable {
         byte[] a = new byte[0];