Broadcast state restoration for BroadcastProcessFunction

[Alexis Sarda-Espinosa <sa...@gmail.com>]

Hello,

I wrote a test for a broadcast function to check how it handles broadcast
state during retries [1] (the gist only shows a subset of the test in
Kotlin, but it's hopefully understandable). The test will not pass unless
my function also implements CheckpointedFunction, although those
interface's methods' implementations can be empty - the state is empty in
this case, even though its descriptor is registered with the harness.

Is this requirement specific to the test harness API?
Otherwise BaseBroadcastProcessFunction should implement
CheckpointedFunction, maybe with empty default methods, no?

[1] https://gist.github.com/asardaes/b804b7ed04ace176881189c3d1cf842a

Regards,
Alexis.