tests: query for nested interface

[BarryThePenguin]

I added a field and query to the tests that reproduces the issue I've been facing

I fixed my original issue by adding a isList argument to resolveInterface(), similar to resolveUnion(). This allows resolveInterface() to resolve a field that is a list with resolveList().

Fixes #55

[jneurock]

@BarryThePenguin, thanks for opening this PR! Is the intention to add a failing test or is it to fully fix the issue you reported? Thanks!

[BarryThePenguin]

It was a failing test originally, just the schema changes alone were enough to reproduce the issue.

I ended up fixing my original issue by using resolveList() in my custom field resolver, so I had a go at including that in resolveInterface() to see if that would fix the tests.

I'll have a go at separating the two commits 👀

[jneurock]

Cool. Don't feel you have to separate the commits into separate PRs, if that's what you meant. Feel free to update the PR title and description to match the changes and mention that it fixes your issue # and all should be good. Thanks!