add a new method that return the mapped properties

There are some implementations that use the doctrine metadata to get the properties of a entity (DoctrineObject), and it currently uses the getFieldNames and getAssociationNames methods to retrieve and merge it. 

Since the embeddables feature was added, that method will return more than one metadata for each embeddable property, and then the hydrator can never find the appropriate setter for that property.

This method allows some implementation to retrieve all mapped fields from an entity, something that can't be done using get_class_vars for example.

Of course this implementation could be done in the hydrator, but i don't think it is its responsibility to filter and merge data received from the ClassMetadata. Since you have methods to retrieve the metadata formatted as the database structure, you should also have methods to retrieve the information to the other side, in object structure.
Directly define this in the assertion