• Setting up another custom graphql express app from scratch. It’s possible to add custom middleware using graphql-middleware. This lets us write functions that can called before every resolver. Example boilerplate for what custom graphql middleware looks like:

export const log = async (
  resolver: any,
  parent: any,
  args: any,
  context: any,
  info: any
) => {
  if (!parent) {
    console.log("Start Logging");
  }
  const result = await resolver(parent, args, context, info);
  console.log("finished call to resolver");
  return result;
};

• Learning how to write unit test for graphql query resolvers

  1. write a testGraphQLQuery wrapper function, takes the schema, source and variableValues :

  import { graphql, GraphQLSchema } from "graphql";
  import { Maybe } from "graphql/jsutils/Maybe";
  
  interface Options {
    schema: GraphQLSchema;
    source: string;
    variableValues?: Maybe<{ [key: string]: any }>;
  }
  
  export const testGraphQLQuery = async ({
    schema,
    source,
    variableValues,
  }: Options) => {
    return graphql({
      schema,
      source,
      variableValues,
    });
  };

  2. This can then be use in a jest test suite. Using the makeExecutableSchema function we can pass in our real type definitions and resolvers as the schema parameter.
  3. we can pass in a real stringified Graphql query for the source parameter
  4. we can pass in an arbitary argument the graphql query accepts as the variableValues parameter. Example code:

  import typeDefs from "./typeDefs";
  import resolvers from "./resolvers";
  import { makeExecutableSchema } from "graphql-tools";
  import faker from "faker";
  import { testGraphQLQuery } from "./testGraphQLquery";
  import { addMockFunctionsToSchema } from "apollo-server-express";
  
  describe("test getting a user", () => {
    const GetUser = `
      query GetUser($id: ID!){
        getUser(id: $id){
          id
          username
          email
        }
      }
    `;
    it("get the desired user", async () => {
      const schema = makeExecutableSchema({ typeDefs, resolvers });
      const userId = faker.random.alphaNumeric(20);
      const username = faker.internet.userName();
      const email = faker.internet.email();
      const mocks = {
        User: () => ({
          id: userId,
          username,
          email,
        }),
      };
      addMockFunctionsToSchema({ schema, mocks });
  
      const queryResponse = await testGraphQLQuery({
        schema,
        source: GetUser,
        variableValues: { id: faker.random.alphaNumeric(20) },
      });
  
      const result = queryResponse.data ? queryResponse.data.getUser : null;
  
      expect(result).toEqual({
        id: userId,
        username,
        email,
      });
    });
  });