@Override
    public String toString() {
        MoreObjects.ToStringHelper helper = MoreObjects.toStringHelper(this);
        helper.addValue(toString(null, null));
        return helper.toString();
    }
@Test
    public void testToStringWhenThereAreZeroInputs() {
        Transaction tx = new Transaction();
        assertTrue(tx.toString().contains("No inputs!"));
    }