public static boolean isBlank(CharSequence s) {
        return skipSpaceTab(s, 0, s.length()) == s.length();
    }
@Test
    public void isBlank() {
        assertTrue(Characters.isBlank(""));
        assertTrue(Characters.isBlank(" "));
        assertTrue(Characters.isBlank("\t"));
        assertTrue(Characters.isBlank(" \t"));
        assertFalse(Characters.isBlank("a"));
        assertFalse(Characters.isBlank("\f"));
    }