@Test
public void testToBase64EnvelopeXdrBuilderNoSignatures() throws FormatException, IOException {

    // GBPMKIRA2OQW2XZZQUCQILI5TMVZ6JNRKM423BSAISDM7ZFWQ6KWEBC4
    KeyPair source = KeyPair.fromSecretSeed("SCH27VUZZ6UAKB67BDNF6FA42YMBMQCBKXWGMFD5TZ6S5ZZCZFLRXKHS");
    KeyPair destination = KeyPair.fromAccountId("GDW6AUTBXTOC7FIKUO5BOO3OGLK4SF7ZPOBLMQHMZDI45J2Z6VXRB5NR");
    Account account = new Account(source, 2908908335136768L);
    Transaction transaction = new Transaction.Builder(account)
            .addOperation(new CreateAccountOperation.Builder(destination, "2000").build())
            .build();
    try {
        transaction.toEnvelopeXdrBase64();
        fail();
    } catch (RuntimeException exception) {
        assertTrue(exception.getMessage().contains("Transaction must be signed by at least one signer."));
    }
}