TestPipeline has now been decoupled from only working with the TestDataflowPipelineRunner and DirectPipelineRunner.
This allows for Beam Flink and Spark runners to use TestPipeline and run the set of validation tests marked with @Category(RunnableOnService.class). More details in TestPipeline <https://github.com/apache/incubator-beam/blob/master/sdks/java/core/src/main/java/com/google/cloud/dataflow/sdk/testing/TestPipeline.java#L42> and an example in TestDataflowPipelineRunner <https://github.com/apache/incubator-beam/blob/6ab55554cb9bf19cc6b62ac379dab4322150e637/sdks/java/core/src/main/java/com/google/cloud/dataflow/sdk/testing/TestDataflowPipelineRunner.java#L55> .
