mb_addslashes.php

<?php
/**
 * addslashes() for multi-byte characters
 *
 * @param  string $input Input characters
 * @param  string $enc   Internal encoding (optional)
 * @return string        Charcters added slashes
 */
function mb_addslashes($input, $enc = NULL)
{
    if (is_null($enc)) {
        $enc = mb_internal_encoding();
    }
    $len = mb_strlen($input, $enc);
    $result = '';
    for ($i = 0; $i < $len; $i++)
    {
        $char = mb_substr($input, $i, 1, $enc);
        if (strlen($char) === 1) {
            $char = addslashes($char);
        }
        $result .= $char;
    }
    return $result;
}

mb_addslashes_test.php

<?php
require_once 'PHPUnit/Framework.php';
require_once 'mb_addslashes.php';

define('INTERNAL_ENCODING', 'UTF-8');

mb_language('Japanese');
ini_set('mbstring.script_encoding', INTERNAL_ENCODING);
ini_set('mbstring.internal_encoding', INTERNAL_ENCODING);

class MbAddslashesTest extends PHPUnit_Framework_TestCase
{
    public function setUp()
    {
        $this->input    = "これは \"mb_addslashes()\" の'テスト'です。\0\\表能ソ。\\";
        $this->expected = "これは \\\"mb_addslashes()\\\" の\\'テスト\\'です。\\0\\\\表能ソ。\\\\";
        $this->encodings = array('UTF-8', 'EUC-JP', 'SJIS', 'SJIS-win');
    }

    public function testAll()
    {
        foreach ($this->encodings as $enc)
        {
            $this->_test($enc);
        }
    }

    private function _test($enc)
    {
        $input    = mb_convert_encoding($this->input, $enc, INTERNAL_ENCODING);
        $expected = mb_convert_encoding($this->expected, $enc, INTERNAL_ENCODING);
        $output   = mb_addslashes($input);
        $this->assertEquals($output, $this->expected, "The output characters should match with the expected one on '{$enc}'.");
    }
}

mb_addslashes_test_sjis.php

<?php
require_once 'PHPUnit/Framework.php';
require_once 'mb_addslashes.php';

define('INTERNAL_ENCODING', 'SJIS');

mb_language('Japanese');
ini_set('mbstring.script_encoding', INTERNAL_ENCODING);
ini_set('mbstring.internal_encoding', INTERNAL_ENCODING);

class MbAddslashesTestSjis extends PHPUnit_Framework_TestCase
{
    public function setUp()
    {
        $bs   = pack("H*", '5c');
        $apos = pack("H*", '27');
        $quot = pack("H*", '22');
        $null = pack("H*", '00');
        $hyo  = pack("H*", '955c');
        $so   = pack("H*", '835c');
        $nou  = pack("H*", '945c');

        $this->input    = array(
            $bs,
            $apos,
            $quot,
            $null,
            $hyo,
            $so,
            $nou
        );
        $this->expected = array(
            "\\{$bs}",
            "\\{$apos}",
            "\\{$quot}",
            pack("H*", '5c30'),
            $hyo,
            $so,
            $nou
        );
        $this->input[]    = join('', $this->input);
        $this->expected[] = join('', $this->expected);
        $this->encodings = array('UTF-8', 'EUC-JP', 'SJIS', 'SJIS-win');
    }

    public function testAll()
    {
        foreach ($this->encodings as $enc)
        {
            foreach ($this->input as $i => $in)
            {
                $this->_test($in, $this->expected[$i], $enc);
            }
        }
    }

    private function _test($in, $exp, $enc)
    {
        $input    = mb_convert_encoding($in, $enc, INTERNAL_ENCODING);
        $expected = mb_convert_encoding($exp, $enc, INTERNAL_ENCODING);
        $output   = mb_addslashes($input);
        $this->assertEquals($output, $expected, "The output characters should match with the expected one on '{$enc}'.");
    }
}