public static String truncateContent(String content) {
        if (content == null) {
            return "";
        } else if (content.length() <= SHOW_CONTENT_SIZE) {
            return content;
        } else {
            return content.substring(0, SHOW_CONTENT_SIZE) + "...";
        }
    }
@Test
    void testTruncateContent() {
        String content = "aa";
        String actual = ContentUtils.truncateContent(content);
        assertEquals(content, actual);
    }