@Test
  public void remembersOneReceipt() throws Exception {
    Receipt receipt = new Receipt(123);

    repository.add(receipt);

    List<Receipt> all = repository.findAll();
    assertEquals(1, all.size());
    assertEquals(receipt, all.get(0));
  }
  @Test
  public void remembersTwoReceipts() throws Exception {
    Receipt first = new Receipt(111);
    Receipt second = new Receipt(222);

    repository.add(first);
    repository.add(second);

    List<Receipt> all = repository.findAll();
    assertEquals(2, all.size());
    assertEquals(first, all.get(0));
    assertEquals(second, all.get(1));
  }