String result = StringUtil.join(",", "a,b", "c,d", "e,f");
        assertEquals("a,b,c,d,e,f", result);
    }

    @Test
    @DisplayName("Should handle empty array")
    void testJoinEmptyArray() {
        CharSequence[] empty = new CharSequence[0];
        String result = StringUtil.join(",", empty);
        assertEquals("", result);
    }

    @Test