While working on #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, I discovered a rather nasty problem with the xml format. On the (de)normalizer side, not the encoder/decoder side.
STR:
$serialized_test = $this->serializer->serialize($node, 'xml');
$unserialized_test = $this->serializer->deserialize($serialized_test, get_class($node), 'xml');
That should serialize a Node entity to the xml format and deserialize it again.
What actually happens: Symfony\Component\Serializer\Exception\UnexpectedValueException: A string must be provided as a bundle value., thrown at core/modules/serialization/src/Normalizer/EntityNormalizer.php:74.
For failing test, please await #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method.
