diff --git a/index.js b/index.js
index 8fd46db..dc206a4 100644
--- a/index.js
+++ b/index.js
@@ -3,9 +3,10 @@
 /**
  * Module dependencies.
  */
-var methods = require('methods');
-var Test = require('./lib/test');
-var http = require('http');
+const methods = require('methods');
+const http = require('http');
+const Test = require('./lib/test.js');
+const agent = require('./lib/agent.js');
 
 /**
  * Test against the given `app`,
@@ -16,7 +17,7 @@ var http = require('http');
  * @api public
  */
 module.exports = function(app) {
-  var obj = {};
+  const obj = {};
 
   if (typeof app === 'function') {
     app = http.createServer(app); // eslint-disable-line no-param-reassign
@@ -42,4 +43,4 @@ module.exports.Test = Test;
 /**
  * Expose the agent function
  */
-module.exports.agent = require('./lib/agent');
+module.exports.agent = agent;
diff --git a/lib/agent.js b/lib/agent.js
index c6ee786..0afb7c7 100644
--- a/lib/agent.js
+++ b/lib/agent.js
@@ -4,16 +4,10 @@
  * Module dependencies.
  */
 
-var Agent = require('superagent').agent;
-var methods = require('methods');
-var http = require('http');
-var Test = require('./test');
-
-/**
- * Expose `Agent`.
- */
-
-module.exports = TestAgent;
+const { agent: Agent } = require('superagent');
+const methods = require('methods');
+const http = require('http');
+const Test = require('./test.js');
 
 /**
  * Initialize a new `TestAgent`.
@@ -50,7 +44,7 @@ TestAgent.prototype.host = function(host) {
 // override HTTP verb methods
 methods.forEach(function(method) {
   TestAgent.prototype[method] = function(url, fn) { // eslint-disable-line no-unused-vars
-    var req = new Test(this.app, method.toUpperCase(), url, this._host);
+    const req = new Test(this.app, method.toUpperCase(), url, this._host);
     req.ca(this._ca);
     req.cert(this._cert);
     req.key(this._key);
@@ -69,3 +63,9 @@ methods.forEach(function(method) {
 });
 
 TestAgent.prototype.del = TestAgent.prototype.delete;
+
+/**
+ * Expose `Agent`.
+ */
+
+module.exports = TestAgent;
diff --git a/lib/test.js b/lib/test.js
index 58fa87c..d835fbd 100644
--- a/lib/test.js
+++ b/lib/test.js
@@ -10,6 +10,8 @@ const { Server } = require('https');
 const { deepStrictEqual } = require('assert');
 const { Request } = require('superagent');
 
+/** @typedef {import('superagent').Response} Response */
+
 class Test extends Request {
   /**
    * Initialize a new `Test` with the given `app`,
@@ -111,18 +113,16 @@ class Test extends Request {
    * @api public
    */
   end(fn) {
-    const self = this;
     const server = this._server;
-    const end = Request.prototype.end;
 
-    end.call(this, function (err, res) {
+    super.end((err, res) => {
+      const localAssert = () => {
+        this.assert(err, res, fn);
+      };
+
       if (server && server._handle) return server.close(localAssert);
 
       localAssert();
-
-      function localAssert() {
-        self.assert(err, res, fn);
-      }
     });
 
     return this;
diff --git a/test/supertest.js b/test/supertest.js
index 0a77dec..7561d1f 100644
--- a/test/supertest.js
+++ b/test/supertest.js
@@ -1,6 +1,5 @@
 'use strict';
 
-const request = require('..');
 const https = require('https');
 const fs = require('fs');
 const path = require('path');
@@ -9,6 +8,7 @@ const express = require('express');
 const bodyParser = require('body-parser');
 const cookieParser = require('cookie-parser');
 const nock = require('nock');
+const request = require('../index.js');
 
 process.env.NODE_TLS_REJECT_UNAUTHORIZED = '0';