Github user StephanEwen commented on the issue:
https://github.com/apache/flink/pull/5645
I added a way to reset the flag into its original state (prior to assertion
activation) and used that to test that the concurrency check is not active by
default. The `KryoSerializerConcurrencyTest` tests the default test setting
(concurrency checks on), the `KryoSerializerConcurrencyCheckInactiveITCase`
tests the general default (concurrency checks off).---
