The current TypeSerializerTestBase does not cover several aspects related to upgrading / snapshotting and restoring Flink's serializers. That includes:
- A serializer can be snapshotted and then restored without issues. The restored serializer should be able to correctly read data written by the snapshotted serializer.
- A serializer's snapshotted configuration can be migrated from previous Flink versions.
- A serializer works with different kinds of state backends.
This new proposed test base should go into flink-tests, with a coverage check that all Flink's TypeSerializers have a corresponding subclass for the test base.