rdflib

I believe turtle does not handle quads, but our default serialization format for ConjunctiveGraph is turtle as turtle does not override the default for Graph, I guess we should probably change this, question is to what.

I think TriG would make most sense, but the other option is n3.

I'm submitting a

• [x ] bug report.

Current Behaviour:

After #249
Trying to run tests with pytest tests/rdf_tests/test_rdf_basic.py -k test_rdf_runner -s, you get a report file with all the tests run.
Some tests return errors, for example:

{
    "Basic - Term 7": {
        "input": "basic/data-4.ttl",
        "query": "basic/term-7.rq",
        "error": "Expected {Sele