### Question:
InMemoryPersistenceNavigator implements PersistenceNavigator { @Override public void notifyTruncation(long seqNum) throws IOException { if (seqNum <= 0) { throw new IllegalArgumentException("InMemoryPersistenceNavigator#notifyTruncation"); } truncateIndex(seqNum); } InMemoryPersistenceNavigator(BytePersistence persistence, SequentialEntryCodec<E> codec);  InMemoryPersistenceNavigator(BytePersistence persistence, SequentialEntryCodec<E> codec, long offset); void setMaxEntrySeek(int numberOfEntries); @Override void notifyLogging(long seqNum, long byteAddress); @Override void addToIndex(long seqNum, long address); @Override void notifyTruncation(long seqNum); @Override long getAddressOfEntry(long seqNum); @Override InputStream getStreamAtSeqNum(long seqNum); @Override InputStream getStreamAtFirstEntry(); @Override InputStream getStreamAtLastEntry();  }### Answer:
@Test(expected = Exception.class) public void throwsAnExceptionIfAskedToTruncateToSeqNumZero() throws Exception { navigator.notifyTruncation(0); }