@Test public void isDigitOnly() {

    assertTrue("input only digit should return true", TextUtils.isDigitOnly("12346"));
    assertTrue("input only digit should return true", TextUtils.isDigitOnly("222222222"));
    assertFalse("input not only digit should return false", TextUtils.isDigitOnly("123adc"));
    assertFalse("empty should return false", TextUtils.isDigitOnly(""));
}