### Question:
ReceiptStoreImpl implements ReceiptStore { @Override public TransactionInfo get(byte[] transactionHash){ List<TransactionInfo> txs = getAll(transactionHash); if (txs.isEmpty()) { return null; } return txs.get(txs.size() - 1); } ReceiptStoreImpl(KeyValueDataSource receiptsDS); @Override void add(byte[] blockHash, int transactionIndex, TransactionReceipt receipt); @Override TransactionInfo get(byte[] transactionHash); @Override TransactionInfo get(byte[] transactionHash, byte[] blockHash, BlockStore store); @Override TransactionInfo getInMainChain(byte[] transactionHash, BlockStore store); @Override List<TransactionInfo> getAll(byte[] transactionHash); @Override void saveMultiple(byte[] blockHash, List<TransactionReceipt> receipts);  }### Answer:
@Test public void getUnknownKey() { ReceiptStore store = new ReceiptStoreImpl(new HashMapDB()); byte[] key = new byte[] { 0x01, 0x02 }; TransactionInfo result = store.get(key); Assert.assertNull(result); }
@Test public void getUnknownTransactionByBlock() { ReceiptStore store = new ReceiptStoreImpl(new HashMapDB()); TransactionReceipt receipt = createReceipt(); byte[] blockHash = Hex.decode("010203040506070809"); TransactionInfo result = store.get(receipt.getTransaction().getHash().getBytes(), blockHash, null); Assert.assertNull(result); }