String result = StringUtil.join(longDelimiter, "A", "B");
        assertEquals("A" + longDelimiter + "B", result);
    }

    @Test
    @DisplayName("Should preserve element order")
    void testJoinPreservesOrder() {
        String result = StringUtil.join(",", "z", "y", "x", "w", "v");
        assertEquals("z,y,x,w,v", result);
    }

    @Test
    @DisplayName("Should handle delimiter as CharSequence subtype")