One of the tests in the new DatasetSink can fail unexpectedly. It tests that the background process rolls the backing files correctly, waiting until the roller should have run and then reading the file. The part that fails is just after the initial call to process(), the test asserts that the records are not yet available. If for some reason the background thread has run and rolled the file, it will fail although everything works correctly.
This was introduced when the rolling was changed to be proactive. Lazy rolling prevented a race.