### Question:
TransactionPool { public boolean isKnown(byte[] hash) { return ByteUtil.contains(known, hash); } private  TransactionPool(int initialCapacity); static TransactionPool getInstance(); synchronized int inject(Transaction tx); boolean isKnown(byte[] hash); int pending(); void clear(); synchronized void drop(Transaction tx); synchronized ArrayList<Transaction> consume(int limit, HashSet<byte[]> avoid);  }### Answer:
@Test public void isKnown() { inject(); Assert.assertTrue(TransactionPool.getInstance().isKnown(tx1.getHash())); pool.drop(tx2); Assert.assertTrue(!TransactionPool.getInstance().isKnown(tx2.getHash())); }