Be more careful with content generation in test_write_replay
When using the object_dicts() strategy, we often end up not generating any
contents; This works because the replayer.process
call is within a loop,
guarded with the length of the queue.
If the queue is empty, replayer.process
is never called, but the test is also
useless. So we add an assertion to that effect.
Depends on !121 (closed).
Test Plan
updated tox tests with new asserts
Migrated from D2797 (view on Phabricator)