JpnForPhp\Helper\Helper::extractKanji PHP Method

    public static function extractKanji($str, $length = 0)
    {
        // No length given, extract kanji substrings as it is.
        if (!$length) {
            return preg_split(self::PREG_PATTERN_NOT_KANJI, $str, 0, PREG_SPLIT_NO_EMPTY);
        }
        // Otherwise...
        // remove any non kanji characters and split the remaining string as per
        // the given length
        $str = preg_replace(self::PREG_PATTERN_NOT_KANJI, "", $str);
        return self::split($str, $length);
    }

 public function testExtractKanjiWithLengthEqualsNWhenMixed()
 {
     $result = Helper::extractKanji($this->mixCharacters, 2);
     $this->assertEquals(array('今日', '学校'), $result);
 }