add test case for clone function

test/strategies.test.js

@@ -1,6 +1,7 @@
 'use strict';
 
 var request = require('../');
+const http = require('http');
 var t = require('chai').assert;
 
 describe('RetryStrategies', function () {
@@ -43,6 +44,38 @@ describe('RetryStrategies', function () {
       });
     });
 
+    it('should not clone `options.agent`', function (done) {
+      const agent = new http.Agent({ keepAlive: true });
+      const cloneable = { a: true };
+      var strategy = function (err, response, body, options) {
+        options.url = 'http://www.filltext.com/?rows=1&err=200'; //overwrite url to return 200
+        t.strictEqual(agent, options.agent);
+        t.deepEqual(cloneable, options.cloneable);
+        t.notEqual(cloneable, options.cloneable);
+        return {
+          mustRetry: true,
+          options: options,
+        };
+      };
+
+      request({
+        url: 'http://www.filltext.com/?rows=1&err=500', // returns a 500 status
+        maxAttempts: 3,
+        agent: agent,
+        retryDelay: 100,
+        cloneable: cloneable,
+        retryStrategy: strategy
+      }, function(err, response, body) {
+        if(err) done(err);
+
+        t.strictEqual(200, response.statusCode);
+        t.strictEqual(agent, this.options.agent);
+        t.deepEqual(cloneable, this.options.cloneable);
+        t.notEqual(cloneable, this.options.cloneable);
+        done();
+      });
+    });
+
     it('should not overwrite `options` object if strategy did not returned it', function (done) {
       var strategy = function (err, response, body, options) {
         options.url = 'http://www.filltext.com/?rows=1&err=200'; //overwrite url to return 200