Type-safe mocks, resolvers, and store

[aaronadamsCA]

@graphql-tools/mock should be able to consume types generated by GraphQL Codegen to provide fully type-safe signatures for mocks, resolvers, and the mock store.

Mocks

The exported IMocks type doesn't seem to work correctly.

We're using this Mocks type locally instead and it works pretty well, giving us type checking and autocomplete on our mock data:

import type { ResolversTypes } from "#graphql-codegen/typescript-resolvers";

type Mocks = {
  [T in keyof ResolversTypes]?: () => DeepPartial<ResolversTypes[T]>;
};

type DeepPartial<T> =
  T extends Promise<infer U> ? Awaited<U>
  : T extends (infer U)[] ? DeepPartial<U>[] | undefined[]
  : T extends object ? { [P in keyof T]?: DeepPartial<T[P]> }
  : T;

Resolvers

Mock resolvers differ from real resolvers in at least two ways:

• The source parameter is always a Ref instead of a parent object.
• The return value can substitute a Ref in place of a result object.

We're using this MockResolvers type locally, it's far from perfect but it's a good start:

import type { Ref } from "@graphql-tools/mock";
import type { GraphQLResolveInfo } from "graphql";

import type { Resolver, Resolvers } from "#graphql-codegen/typescript-resolvers";

type AllResolvers = Required<Resolvers>;
type AllFields<TTypeName extends keyof AllResolvers> = Required<
  AllResolvers[TTypeName]
>;

type MockResolvers = {
  [TTypeName in keyof AllResolvers]?: {
    [TFieldName in keyof AllFields<TTypeName>]?: AllFields<TTypeName>[TFieldName] extends (
      Resolver<infer TResult, never, infer TContext, infer TArgs>
    ) ?
      (
        source: Ref,
        args: TArgs,
        context: TContext,
        info: GraphQLResolveInfo,
      ) => TResult extends unknown[] ? TResult | Ref[] : TResult | Ref
    : never;
  };
};

Store

Right now the mock store is completely untyped, all of its get and set signatures use unknown. I think it should be possible to pass the generated Resolvers type to create a fully-typed store.