### Question:
Datastore { public RollbackResponse rollback(RollbackRequest request) throws DatastoreException { try (InputStream is = remoteRpc.call("rollback", request)) { return RollbackResponse.parseFrom(is); } catch (IOException exception) { throw invalidResponseException("rollback", exception); } } Datastore(RemoteRpc remoteRpc); void resetRpcCount(); int getRpcCount(); AllocateIdsResponse allocateIds(AllocateIdsRequest request); BeginTransactionResponse beginTransaction(BeginTransactionRequest request); CommitResponse commit(CommitRequest request); LookupResponse lookup(LookupRequest request); ReserveIdsResponse reserveIds(ReserveIdsRequest request); RollbackResponse rollback(RollbackRequest request); RunQueryResponse runQuery(RunQueryRequest request);  }### Answer:
@Test public void rollback() throws Exception { RollbackRequest.Builder request = RollbackRequest.newBuilder(); request.setTransaction(ByteString.copyFromUtf8("project-id")); RollbackResponse.Builder response = RollbackResponse.newBuilder(); expectRpc("rollback", request.build(), response.build()); }