s2sTesting: random number moved to global (prebid#3851)

* s2sTesting: random number moved to global

We got a request that if if 10% of bidderA and 10% of bidderB should be server-side, they should be the same 10% of requests.

This is a simple approach to the change that implies that the same page experience only throws one random number for the purposes of s2sTesting. i.e. if there are dynamic ads on the page, all newly created ads on the page will continue to use the same number. This is ok from the purposes of the s2sTesting module.

* Added get for randNum + fix lint & tests

* update to remove getter

* remove log

* update test

modules/s2sTesting.js

@@ -11,6 +11,7 @@ s2sTesting.CLIENT = CLIENT;
 
 var testing = false; // whether testing is turned on
 var bidSource = {}; // store bidder sources determined from s2sConfing bidderControl
+s2sTesting.globalRand = Math.random(); // if 10% of bidderA and 10% of bidderB should be server-side, make it the same 10%
 
 // load s2sConfig
 config.getConfig('s2sConfig', config => {
@@ -82,7 +83,7 @@ s2sTesting.getSource = function(sourceWeights = {}, bidSources = [SERVER, CLIENT
   });
   if (!totWeight) return; // bail if no source weights
   // choose a source randomly based on weights
-  var rndWeight = Math.random() * totWeight;
+  var rndWeight = s2sTesting.globalRand * totWeight;
   for (var i = 0; i < bidSources.length; i++) {
     let source = bidSources[i];
     // choose the first source with an incremental weight > random weight

test/spec/modules/s2sTesting_spec.js

@@ -1,30 +1,14 @@
 import s2sTesting from 'modules/s2sTesting';
 import { config } from 'src/config';
-import find from 'core-js/library/fn/array/find';
-
-var events = require('src/events');
-var CONSTANTS = require('src/constants.json');
-const BID_ADJUSTMENT = CONSTANTS.EVENTS.BID_ADJUSTMENT;
 
 var expect = require('chai').expect;
 
 describe('s2sTesting', function () {
-  let mathRandomStub;
-  let randomNumber = 0;
-
-  beforeEach(function () {
-    mathRandomStub = sinon.stub(Math, 'random').callsFake(() => { return randomNumber; });
-  });
-
-  afterEach(function () {
-    mathRandomStub.restore();
-  });
-
   describe('s2sTesting.getSource', function () {
     // helper function to set random number and get the source
     function getExpectedSource(randNumber, sourceWeights, sources) {
       // set random number for testing
-      randomNumber = randNumber;
+      s2sTesting.globalRand = randNumber;
       return s2sTesting.getSource(sourceWeights, sources);
     }
 
@@ -93,7 +77,7 @@ describe('s2sTesting', function () {
     describe('setting source through s2sConfig', function () {
       beforeEach(function () {
         // set random number for testing
-        randomNumber = 0.7;
+        s2sTesting.globalRand = 0.7;
       });
 
       it('does not work if testing is "false"', function () {
@@ -155,14 +139,58 @@ describe('s2sTesting', function () {
         expect(serverClientBidders.server).to.eql(['rubicon']);
         expect(serverClientBidders.client).to.have.members(['appnexus']);
       });
+
+      it('sends both bidders to same source when weights are the same', function () {
+        s2sTesting.globalRand = 0.01;
+
+        config.setConfig({s2sConfig: {
+          bidders: ['rubicon', 'appnexus'],
+          testing: true,
+          bidderControl: {
+            rubicon: {bidSource: {server: 1, client: 99}},
+            appnexus: {bidSource: {server: 1, client: 99}}
+          }}});
+        expect(s2sTesting.getSourceBidderMap()).to.eql({
+          client: ['rubicon', 'appnexus'],
+          server: []
+        });
+        expect(s2sTesting.getSourceBidderMap()).to.eql({
+          client: ['rubicon', 'appnexus'],
+          server: []
+        });
+        expect(s2sTesting.getSourceBidderMap()).to.eql({
+          client: ['rubicon', 'appnexus'],
+          server: []
+        });
+
+        config.setConfig({s2sConfig: {
+          bidders: ['rubicon', 'appnexus'],
+          testing: true,
+          bidderControl: {
+            rubicon: {bidSource: {server: 99, client: 1}},
+            appnexus: {bidSource: {server: 99, client: 1}}
+          }}});
+        expect(s2sTesting.getSourceBidderMap()).to.eql({
+          server: ['rubicon', 'appnexus'],
+          client: []
+        });
+        expect(s2sTesting.getSourceBidderMap()).to.eql({
+          server: ['rubicon', 'appnexus'],
+          client: []
+        });
+        expect(s2sTesting.getSourceBidderMap()).to.eql({
+          server: ['rubicon', 'appnexus'],
+          client: []
+        });
+      });
     });
 
     describe('setting source through adUnits', function () {
       beforeEach(function () {
         // reset s2sconfig bid sources
         config.setConfig({s2sConfig: {testing: true}});
         // set random number for testing
-        randomNumber = 0.7;
+        s2sTesting.globalRand = 0.7;
       });
 
       it('sets one bidder source from one adUnit', function () {
@@ -280,7 +308,7 @@ describe('s2sTesting', function () {
         // reset s2sconfig bid sources
         config.setConfig({s2sConfig: {testing: true}});
         // set random number for testing
-        randomNumber = 0.7;
+        s2sTesting.globalRand = 0.7;
       });
 
       it('should get sources from  both', function () {