Cloud computing has emerged as a multi-tenant resource sharing platform, which allows different service providers to deliver software as services in an economical way. However, for many security sensitive applications such as critical data processing, we must provide necessary security protection for migrating those critical application services into shared open cloud infrastructures. In this paper, we present RunTest, a scalable runtime integrity attestation framework to assure the integrity of dataflow processing in cloud infrastructures. RunTest provides light-weight application-level attestation methods to dynamically verify the integrity of data processing results and pinpoint malicious service providers when inconsistent results are detected. We have implemented RunTest within IBM System S dataflow processing system and tested it on NCSU virtual computing lab. Our experimental results show that our scheme is effective and imposes low performance impact for dataflow processing in the cloud infrastructure.