apache_beam.io.avroio_test.TestAvro.test_dynamic_work_rebalancing_exhaustive is very slow

$ python setup.py test -s apache_beam.io.avroio_test.TestFastAvro.test_dynamic_work_rebalancing_exhaustive
test_dynamic_work_rebalancing_exhaustive (apache_beam.io.avroio_test.TestFastAvro) ... WARNING:root:After 101 concurrent splitting trials at item #2, observed only failure, giving up on this item
WARNING:root:After 101 concurrent splitting trials at item #21, observed only failure, giving up on this item
WARNING:root:After 101 concurrent splitting trials at item #22, observed only failure, giving up on this item
WARNING:root:After 1014 total concurrent splitting trials, considered only 25 items, giving up.
ok
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Ran 1 test in 172.223s
 

$ python setup.py test -s apache_beam.io.avroio_test.TestAvro.test_dynamic_work_rebalancing_exhaustive
test_dynamic_work_rebalancing_exhaustive (apache_beam.io.avroio_test.TestAvro) ... ok

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Ran 1 test in 0.623s

OK