Arduino coding crc

How to test the ID-12 RFID tag reader crc and checksum code on arduino board without the ID-12 reader?
I’m using the serial monitor and in the space for send I just put an ascii or hex value and then press enter but no output display. If my method is wrong please let me know. I am also need more understandable explanation about this code as I am still new in Arduino c++ coding.
I’m sorry as i am quite a slow learner.

This is the code I copy from Learning Tab,Playground from arduino.cc

// RFID reader ID-12 for Arduino 
// Based on code by BARRAGAN
// and code from HC Gilje - 
// Modified for Arduino by djmatic
// Modified for ID-12 and checksum by Martijn The - http://www.martijnthe.nl/
//
// Use the drawings from HC Gilje to wire up the ID-12.
// Remark: disconnect the rx serial wire to the ID-12 when uploading the sketch


void setup() {
 Serial.begin(9600);                                 // connect to the serial port
}

void loop () {
 byte i = 0;
 byte val = 0;
 byte code[6];
 byte checksum = 0;
 byte bytesread = 0;
 byte tempbyte = 0;

 if(Serial.available() > 0) {
   if((val = Serial.read()) == 2) {                  // check for header 
     bytesread = 0; 
     while (bytesread < 12) {                        // read 10 digit code + 2 digit checksum
       if( Serial.available() > 0) { 
         val = Serial.read();
         if((val == 0x0D)||(val == 0x0A)||(val == 0x03)||(val == 0x02)) { // if header or stop bytes before the 10 digit reading 
           break;                                    // stop reading
         }

         // Do Ascii/Hex conversion:
         if ((val >= '0') && (val <= '9')) {
           val = val - '0';
         } else if ((val >= 'A') && (val <= 'F')) {
           val = 10 + val - 'A';
         }

         // Every two hex-digits, add byte to code:
         if (bytesread & 1 == 1) {
           // make some space for this hex-digit by
           // shifting the previous hex-digit with 4 bits to the left:
           code[bytesread >> 1] = (val | (tempbyte << 4));

           if (bytesread >> 1 != 5) {                // If we're at the checksum byte,
             checksum ^= code[bytesread >> 1];       // Calculate the checksum... (XOR)
           };
         } else {
           tempbyte = val;                           // Store the first hex digit first...
         };

         bytesread++;                                // ready to read next digit
       } 
     } 

     // Output to Serial:

     if (bytesread == 12) {                          // if 12 digit read is complete
       Serial.print("5-byte code: ");
       for (i=0; i<5; i++) {
         if (code[i] < 16) Serial.print("0");
         Serial.print(code[i], HEX);
         Serial.print(" ");
       }
       Serial.println();

       Serial.print("Checksum: ");
       Serial.print(code[5], HEX);
       Serial.println(code[5] == checksum ? " -- passed." : " -- error.");
       Serial.println();
     }

     bytesread = 0;
   }
 }
}

I cleaned up your code.
You need to use triple backticks to post code to the forum.
See this post for details.

The serial wire only needs to be disconnected while uploading the sketch. It must be connected while running the tests.

The serial monitor should display output from the computer. You’re only supposed to read it with your eyes.

So if I try to put any data on the serial monitor, there will be no data?