Ouzo\Utilities\Strings::uppercaseFirst PHP Method

    public static function uppercaseFirst($string)
    {
        $first = mb_substr($string, 0, 1);
        return mb_strtoupper($first) . mb_substr($string, 1);
    }

 /**
  * @test
  */
 public function shouldPreserveCaseInRestOfString()
 {
     //given
     $string = "łuKaSz";
     //when
     $uppercaseFirst = Strings::uppercaseFirst($string);
     //then
     $this->assertEquals('ŁuKaSz', $uppercaseFirst);
 }