Check parse . serialize == id for NTriples, Turtle and RDF/XML

[robstewart57]

Discussion moved from #67 (comment) .

serialize . parse == id

Something like this would be a good property check for all three Ntriples, Turtle and RDF/XML formats.

Ideally we'd have:

parse . serialize == id

Since we use the generator instances we already have for RDF graphs in rdf4h. i.e.

1. Use the Arbitrary instances in testsuite/tests/Data/RDF/PropertyTests.hs to generate RDF graphs.

2. Serialise the graph to NTriples, Turle and RDF/XML formats.

3. Parse that data back into RDF graphs in Haskell.

Check the graphs are equivalent.

As you say @wismill , it comes down the how equivalence check is performed. We do have isIsomorphic and isGraphIsomorphic in https://github.com/robstewart57/rdf4h/blob/master/src/Data/RDF/Query.hs .

The problem we have with property based testing of serialize . parse == id, is that we'd need predefined NTriples, Turtle and RDF/XML inputs to parse.