Fix and test schema generation interface

[pmantica1]

No description provided.

[coveralls]

Coverage increased (+0.2%) to 93.68% when pulling cfd45c8 on update-schema-generation-documentation into e24b4eb on master.

[bojanserafimov]

This api has no test coverage. We didn't know that type_id is not the correct name of the argument. Maybe add a test with some small made up schema? For your convenience, here's the input I used that exposed this bug:

    schema_graph = SchemaGraph([
        {
            'name': 'Entity',
            'abstract': True,
            'superClasses': [],
            'properties': [
                {
                    'name': 'name',
                    'type': schema_properties.PROPERTY_TYPE_STRING_ID,
                }
            ]
        },
        {
            'name': 'Animal',
            'abstract': False,
            'superClasses': ['Entity'],
            'properties': [
                {
                    'name': 'net_worth',
                    'type': schema_properties.PROPERTY_TYPE_DECIMAL_ID,
                }
            ]
        },
        {
            'name': 'Location',
            'abstract': False,
            'superClasses': ['Entity'],
            'properties': [
                {
                    'name': 'description',
                    'type': schema_properties.PROPERTY_TYPE_STRING_ID,
                }
            ]
        },
    ])

[obi1kenobi]

Nit: the visual indentation is off by one space (compare string vs default)

[obi1kenobi]

Do we actually need this to be a snapshot test here? This feels like a unit test to me since we have well-defined input and output, and a single function call being tested. Invoking all the snapshot testing machinery feels like overkill for this use case.

[pmantica1]

I think it's a good idea because every time I've made a small change to the way we generate the schema, I've had to print it and then copy paste it into test_helpers. If I introduce this test as an unit test, every time we change the schema we now have to change two things.

[obi1kenobi]

Add a test on the generated schema graph that these properties exist and have their expected values?

[obi1kenobi]

This also doesn't merge cleanly anymore, so I'll hold off on reviewing until you've had a chance to resolve the merge conflicts.