Turn off eager mode in unit tests
Celery has an option called eager mode that switches all task execution from asynchronous to synchronous. We have eager mode turned on during the unit tests. It makes writing tests easier, but it makes it so that our tests cannot detect concurrency issues such as canvas deadlocks or core Celery bugs in handling complex pipelines.
Turning off eager mode in the unit tests would make it more likely that our tests would catch failure modes like what happened with S190510g.