Test how the XML serializer manages startEntity() and endEntity() SAX events. The XML serializer
only ouputs the characters events received between these two events, and totally ignores the
startElement() and endElement() events.
Bogus result: a pipeline with just a file generator followed by
an XML serializer. The file references and entity containing XML markup.
Correct result: a XSL performing an identity transformation
is inserted between the generator and the serializer. It has the effect of removing the
startEntity() and endEntity() events from the SAX stream, and the XML serializer therefore
correcly does its job.