public String generate(int length) {
        StringBuilder sb = new StringBuilder();
        random.ints(length, 0, CHARACTER.length())
                .mapToObj(CHARACTER::charAt)
                .forEach(sb::append);
        return sb.toString();
    }
@Test
    void 주어진_길이에_맞는_랜덤한_문자열을_생성한다() {
        // given
        int length = 8;
        RandomCodeGenerator randomCodeGenerator = new RandomCodeGenerator();

        // when
        String actual = randomCodeGenerator.generate(length);

        // then
        assertThat(actual).matches("[a-zA-Z0-9]{%d}".formatted(length));
    }