How best to test the __resolveReference resolver?

[tjmgregory]

Howdy folks!

As part of our federated gateway, we use the __resolveReference approach to allow service api-books (I'm using fake names/types for ease) to have an entity Book which has a field author: Author, where Author is an entity from service api-authors.

To accomplish this, in api-authors, I have the following:

import { Author, Resolvers, GraphQLRecursivePick } from '../graphql/types'

const resolvers: Resolvers = {
  Author: {
    async __resolveReference(
      { id }: GraphQLRecursivePick<Author, { id: true }>,
    ): Promise<Author> {
      ...
    }
}

How should one test (ideally with the service running, so not unit) this resolver?

Now, no other entity in api-authors has an author: Author field, so we can't hop on the back of an integration test that returns that entity, and include author in the return fields that way.

Ideally too I would prefer not having to add types/resolvers to accomplish this for the sole purpose of testing, as this gives me a less confidence that this would work in production.

What do folks suggest? :) Thanks all!

Edit: Should add that I've scoured high and low for suggestions in the docs and online, but have come up dry 💧

[lennyburdette]

You can pretend to be the gateway and executing the __resolveReference functions by calling the _entities field like this:

query ($representations: [_Any!]!) {
  _entities(representations: $representations) {
    ... on User {
      id
      username
    }
  }
}

which is documented here: https://www.apollographql.com/docs/federation/subgraphs/#query_entities

Hope this helps!

[tjmgregory]

Oh sensational, this is spot on what I have been looking for! Thank you so much, you're a hero 🦸 💪 I'd even scanned over this section but somehow didn't connect the dots 🤦
Thanks again!