Apollo error test

error-test.js

var express = require('express');
var bodyParser = require('body-parser');
var apolloServerExpress = require('apollo-server-express');
var {graphqlExpress, graphiqlExpress} = apolloServerExpress;

var makeExecutableSchema = require('graphql-tools').makeExecutableSchema;

var typeDefs = `
type Query {
  testString: String
}
`;

var resolvers = {
  Query: {
    testString(_, args) {
      return 'Error test';
    },
  },
};

var app = express();

app.use(
  '/graphql',
  bodyParser.json(),
  graphqlExpress({
    schema: makeExecutableSchema({typeDefs, resolvers}),
  })
);
app.use('/graphiql', graphiqlExpress({endpointURL: '/graphql'}));

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  console.log('In 404');
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handler
app.use(function(err, req, res, next) {
  console.log('In error handler');
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.json({err});
});

app.listen(8888, () =>
  console.log(`GraphiQL is now running on http://localhost:${8888}/graphiql`)
);

output.txt

zfriss@BOSMM2TX2V7HTD8 graphql-test $ node error-test.js
GraphiQL is now running on http://localhost:8888/graphiql
In 404
In error handler
Error: Can't set headers after they are sent.
    at validateHeader (_http_outgoing.js:504:11)
    at ServerResponse.setHeader (_http_outgoing.js:511:3)
    at ServerResponse.header (/Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/response.js:730:10)
    at ServerResponse.send (/Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/response.js:170:12)
    at ServerResponse.json (/Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/response.js:256:15)
    at /Users/zfriss/Desktop/Dev/ion/ionstats-server/error-test.js:50:7
    at Layer.handle_error (/Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/router/layer.js:71:5)
    at trim_prefix (/Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/router/index.js:315:13)
    at /Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/Users/zfriss/Desktop/Dev/ion/ionstats-server/node_modules/express/lib/router/index.js:335:12)

#4527 same error with express-session and nest/graphql