switch($matches[0][0]) does the trick. The extra index is necessary as a var_dump() of $matches reveals:

array(2) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "test1"
    [1]=>
    int(0)
  }
  [1]=>
  array(2) {
    [0]=>
    string(1) "1"
    [1]=>
    int(4)
  }
}

As others point out, this is probably not the ideal way to solve the problem, though. There are many other ways, for example:

preg_match('/test([1-5])\./', $baseURL, $m);
return $m ? $m[1] + 1 : 1;

switch($matches[0][0]) does the trick. The extra index is necessary as a var_dump() of $matches reveals:

array(2) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "test1"
    [1]=>
    int(0)
  }
  [1]=>
  array(2) {
    [0]=>
    string(1) "1"
    [1]=>
    int(4)
  }
}

As others point out, this is probably not the ideal way to solve the problem, though. There are many other ways, for example:

preg_match('/test([1-4])\./', $baseURL, $m);
return $m ? $m[1] + 1 : 1;