Looks like more than one are allowed, as defined in the JAR Service
Provider docs (see the *--> in the text below) -
http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider
A service provider identifies itself by placing a provider-configuration
file in the resource directory ME
In writing test cases for the PersistenceProviderResolver and
PersistenceProviderResolverHolder, I discovered that the current
implementation of the resolver will handle multiple providers specified in
the javax.persistence.spi.PersistenceProvider file. However, I expected just
the first one to be
