@Test
 public void toPlainString() {
   assertEquals("20070206001", NumberHelper.toPlainString("2.0070206001E10"));
   assertEquals("", NumberHelper.toPlainString(""));
   assertEquals(" ", NumberHelper.toPlainString(" "));
   assertEquals("1", NumberHelper.toPlainString("1"));
   assertEquals("hallo1", NumberHelper.toPlainString("hallo1"));
 }