Write a PHP program to concat two given strings (lowercase). If there are any double character in new string then omit one character

<?php
function test($s1, $s2)
{
       if (strlen($s1) < 1)
            {
                return $s2;
            }
            if (strlen($s2) < 1)
            {
                return s1;
            }
            return substr($s1, strlen($s1)-1, 1) <> substr($s2, 0, 1) ? $s1 . $s2 : $s1 . substr($s2, 1, strlen($s1)-1);
    }
echo test("abc", "cat")."\n";
echo test("Python", "PHP")."\n";
echo test("php", "php")."\n";