@Test
public void testBuyStocks(TestContext tc) {

  Async async = tc.async();
  service.buy(10, quote("A", 10, 20, 100), ar -> {
    tc.assertTrue(ar.succeeded());
    Portfolio portfolio = ar.result();
    tc.assertEquals(portfolio.getAmount("A"), 10);
    tc.assertEquals(portfolio.getAmount("B"), 0);
    tc.assertEquals(portfolio.getCash(), original.getCash() - 10 * 10);
    async.complete();
  });
}