code: public boolean containsVisibleTextString()
      {
          String s = getText();
          for (int i = 0; i < s.length(); i++)
          {
              char ch = s.charAt(i);
              if (!Character.isSpaceChar(ch))
                  return true;
          }
          return false;
      }
docs: Checks if the box text is visible (it does not contain spaces only). This is not equivalent to isWhitespace() because
  non-beraking spaces are not whitespace characters but they are not visible.
  @return <true> if the box text consists of space characters only