@Override
    public void onDrain(MessageCollector collector, TaskCoordinator coordinator) throws Exception {
      drainCounter++;
    }
End to end integration test to check drain functionality with samza low-level API.
Tests have been annotated with @Ignore as they seem to timeout on the build system.
samza-test/src/test/java/org/apache/samza/test/drain/DrainLowLevelApiIntegrationTest.java