how to e2e test an ApolloServer instance

startTestServer-express.js

import { HttpLink } from 'apollo-link-http';
import * as express from 'express';
import fetch from 'node-fetch';
import { AddressInfo } from 'net';
import { execute } from 'apollo-link';
export { toPromise } from 'apollo-link';

import { ApolloServer } from './';

export const startTestServer = async (server: ApolloServer) => {
  const app = express();
  server.applyMiddleware({ app });
  const httpServer = await app.listen(0);

  const link = new HttpLink({
    uri: `http://localhost:${
      (httpServer.address() as AddressInfo).port
    }/graphql`,
    fetch,
  });

  const executeOperation = ({
    query,
    variables = {},
  }: {
    query: any;
    variables: Record<string, any>;
  }) => execute(link, { query, variables });

  return { link, stop: () => httpServer.close(), graphql: executeOperation };
};