Submitted on behalf of a third-party: add mergeResolvers

[finnigantime]

TODO:

• If this PR is a new feature, reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change. Include a description of your change, link to PR (always) and issue (if applicable). Add your CHANGELOG entry under vNEXT. Do not create a new version number for your change yourself.

Implements #1083.

This PR takes an existing well-publicized gist https://gist.github.com/hellendag/2aa9ad1f9b771f38802760c269bb1b76 (with two small Typescript typing changes) and exposes it as part of graphql-tools. Currently we copy-pasted the gist into our codebase but we don't want to have to maintain it ourselves and keep it in sync with the rest of graphql/graphql-tools. It is generally useful for schema mocking and makes sense to expose in the graphql-tools lib.

[apollo-cla]

@finnigantime: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[finnigantime]

the two typing changes from the original gist are to add | ResolvedValue | ResolverMap here.

A ResolverMap value can be a ResolvedValue directly - no need for a ResolverFunction. This seems to work fine in our testing.

The other change is to allow a ResolverMap value to be another ResolverMap. The ResolverMap can be multilevel. For instance, one test we wrote passes:

    const client = mockClient({
      WorkItem: () => ({
        queue: () => ({
          id: () => 'test-queue-id-1',
        }),
      }),
    });

(here, mockClient is our local mock Apollo client and it calls mergeResolvers() with the first argument being our base set of mock resolvers for all tests, and the second argument being the test-specific resolver override map)

[rhoskal]

Just throwing out a gentle bump here... what's the status of this PR?

[finnigantime]

I would love to get this in. On my end, this is ready to merge. We left a note to @hellendag on the gist to notify. Repo admins - ok to merge this?

[crisu83]

@finnigantime Why are there no unit tests for mergeResolvers?

[smeevil]

Quite interested in this and wondering what is blocking it.

[finnigantime]

Nothing from my end

[yaacovCR]

Wondering about adding to graphql-tools-fork. What does this do that mergeDeep does not?

[yaacovCR]

I see, this runs both resolvers to make sure to return something.

[ardatan]

Thank you @finnigantime for this contribution ! We are planning to merge your code with mergeResolvers from @graphql-toolkit/schema-merging.

[tamlyn]

@graphql-toolkit/schema-merging has become @graphql-tools/merge but the above mock merging function code still hasn't been included AFAICT.