fix: avoid server re-use race conditions

Prevents ECONNRESET when the same HTTP Server is used for more than 3
simultaneous connections.

Closes #709
Closes #844

Ref:

* #846

Author: alxndrsn

index.js

@@ -4,7 +4,6 @@
  * Module dependencies.
  */
 const methods = require('methods');
-const http = require('http');
 let http2;
 try {
   http2 = require('http2'); // eslint-disable-line global-require
@@ -32,15 +31,12 @@ module.exports = function(app, options = {}) {
           'supertest: this version of Node.js does not support http2'
         );
       }
-      app = http2.createServer(app); // eslint-disable-line no-param-reassign
-    } else {
-      app = http.createServer(app); // eslint-disable-line no-param-reassign
     }
   }
 
   methods.forEach(function(method) {
     obj[method] = function(url) {
-      var test = new Test(app, method, url);
+      var test = new Test(app, method, url, options.http2);
       if (options.http2) {
         test.http2();
       }

lib/test.js

@@ -5,10 +5,17 @@
  */
 
 const { inspect } = require('util');
+const http = require('http');
 const { STATUS_CODES } = require('http');
 const { Server } = require('tls');
 const { deepStrictEqual } = require('assert');
 const { Request } = require('superagent');
+let http2;
+try {
+  http2 = require('http2'); // eslint-disable-line global-require
+} catch (_) {
+  // eslint-disable-line no-empty
+}
 
 /** @typedef {import('superagent').Response} Response */
 
@@ -22,9 +29,17 @@ class Test extends Request {
    * @param {String} path
    * @api public
    */
-  constructor (app, method, path) {
+  constructor (app, method, path, optHttp2) {
     super(method.toUpperCase(), path);
 
+    if (typeof app === 'function') {
+      if (optHttp2) {
+        app = http2.createServer(app); // eslint-disable-line no-param-reassign
+      } else {
+        app = http.createServer(app); // eslint-disable-line no-param-reassign
+      }
+    }
+
     this.redirects(0);
     this.buffer();
     this.app = app;

test/supertest.js

@@ -79,6 +79,23 @@ describe('request(app)', function () {
       });
   });
 
+  it('should not ECONNRESET on multiple simultaneous tests', function (done) {
+    const app = express();
+
+    app.get('/', function (req, res) {
+      res.send('hey');
+    });
+
+    const test = request(app);
+
+    const requestCount = 10;
+
+    const requests = [];
+    for (let i = 0; i < requestCount; i += 1) requests.push(test.get('/'));
+
+    global.Promise.all(requests).then(() => done(), done);
+  });
+
   it('should work with an active server', function (done) {
     const app = express();
     let server;