How to extract value of GROUP CHECK BOX in PHP

Below given is PHP script to get value of Selected CHECK BOX from group of CHECK BOX and HTML Code for Group of CHECK BOX

$checkbox_value ="";
$temp =$_POST['test_cb'];

while (list ($key,$val) = @each ($temp)) {
$checkbox_value .= "$val,";
}
?>

<input type="checkbox" name="test_cb[]" value="Test1" />Test1
<input type="checkbox" name="test_cb[]" value="Test2" />Test2