src/Mutator/Number/IntegerValue.php
public static function getMutation(array &$tokens, $index)
    {
        $num = (integer) $tokens[$index][1];
        if ($num == 0) {
            $replace = 1;
        } elseif ($num == 1) {
            $replace = 0;
        } else {
            $replace = $num + 1;
        }
        $tokens[$index] = [
            T_LNUMBER,
            (string) $replace
        ];
    }
public static function getMutation(array &$tokens, $index)
    {
        $num = (integer) $tokens[$index][1];
        if ($num == 0) {
            $replace = 1;
        } elseif ($num == 1) {
            $replace = 0;
        } else {
            $replace = $num + 1;
        }
        $tokens[$index] = [
            T_LNUMBER,
            (string) $replace
        ];
    }
Replace 1 with 0, 0 with 1, or increment.

@param array $tokens
@param int $index
@return array