### Question:
CharSequenceUtil { public static boolean isBlank(CharSequence charSequence) { if (isEmpty(charSequence)) { return true; } for (int i = 0, length = charSequence.length(); i < length; i++) { char ch = charSequence.charAt(i); if (!Character.isWhitespace(ch)) { return false; } } return true; }  static boolean isEmpty(CharSequence charSequence); static boolean isNotEmpty(CharSequence charSequence); static boolean isBlank(CharSequence charSequence); static boolean isNotBlank(CharSequence charSequence);  }### Answer:
@Test public void testIsBlank() { assertTrue(CharSequenceUtil.isBlank(null)); assertTrue(CharSequenceUtil.isBlank("")); assertTrue(CharSequenceUtil.isBlank(" ")); assertTrue(CharSequenceUtil.isBlank(" \t\n\r ")); assertFalse(CharSequenceUtil.isBlank("a")); assertFalse(CharSequenceUtil.isBlank(" a ")); }