อยากสอบถามเรื่องดักค่าว่าง checkbox หน่อยครับ ใครก็ได้ช่วยทีครับ

<script>
function checkRadio(form, GroupName) 
{ 
	var radios = document[form].elements[GroupName];
	
	for (var i=0; i < radios.length; i++)
	{ 
  		if(radios[i].checked)
		{ 
   			return true; 
  		} 
 	}
}

function validform()
{		
	if(!checkRadio("form1","test"))
	{
		alert("Please Select Data");
		return false;
	}
	else
	{
		alert("Select Data OK");
	}
}
</script>
<form id="form1" name="form1" method="post" action="">
  <table width="200" border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td width="27">
      <input type="radio" name="test" id="test" value="1" />
      </td>
      <td width="173">Test 1</td>
    </tr>
    <tr>
      <td>
      <input type="radio" name="test" id="test" value="2" />
      </td>
      <td>Test 2</td>
    </tr>
    <tr>
      <td>
      <input type="radio" name="test" id="test" value="3" />
      </td>
      <td>Test 3</td>
    </tr>
  </table>
  <table width="200" border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td height="40"><input type="submit" name="button" id="button" value="Submit" onclick="return validform();" /></td>
    </tr>
  </table>
</form>