Recent reviews on Encoder and Decoder classes has shown that it is still too easy to make mistakes when creating them. We should add abstract base classes or helper classes that check common codec testing scenarios:
Encode a Flux of objects into a Flux of data buffers. Release the returned data buffers, but make sure that there are not other buffers which are still allocated.
Decode a Flux of data buffers into a Flux of objects. Make sure that all data buffers have been released.
As above, but with an error in the input stream.
As above, but cancel the stream after one received element.