Bad Test

FYI: [this test](https://github.com/graphql-python/sanic-graphql/blob/36a940327071bb0c019d8881d170fd7c7a85713a/tests/test_graphqlview.py#L481) will never run (or it will always run, but it shouldn't).

I'm in the process of porting this to `aiohttp` and found this...

I believe the test is all kinds of wrong.
* its name doesn't match what it does (it has nothing to do with pretty printing)
* I don't understand why 'request' would resolve to `{}`. I'd assume it'd be repr'd to ``

I believe the test **ought to** test that 'CUSTOM CONTEXT' is replaced with an empty dict. at least that's what the code will do when `get_context(request)` is called and it discovers that self.context is not a dict.

Here's my replacement test (note, this isn't written for sanic, but the premise holds):
```
@pytest.mark.asyncio
async def test_context_remapped(self, client, url_builder):
response = await client.get(url_builder(query='{context}'))

_json = await response.json()
assert response.status == 200
assert 'request' in _json['data']['context']
assert 'CUSTOM CONTEXT' not in _json['data']['context']
```