[backend][nodejs] Add seed to random decision

backend/nodejs/package.json

@@ -14,6 +14,7 @@
   },
   "dependencies": {
     "random": "^3.0.3",
+    "seedrandom": "^3.0.5",
     "should": "^13.2.3"
   }
 }

backend/nodejs/random-decision.js

@@ -1,4 +1,5 @@
 const random = require('random');
+const seedrandom = require("seedrandom");
 
 class Choice {
     constructor(name) {
@@ -16,7 +17,8 @@ const choices = [
     new Choice('C')
 ];
 
-exports.getRandomChoice = () => {
+exports.getRandomChoice = (seed = new Date()) => {
+    random.use(seedrandom(seed));
     return choices[random.int(0, choices.length - 1)];
 }
 

backend/nodejs/test/random-decision.js

@@ -3,7 +3,7 @@ const should = require('should');
 const randomDecision = require('../random-decision');
 
 describe('randomDecision', function () {
-    describe('#getRandomChoice', function () {
+    describe('#getRandomChoice()', function () {
         it(`should return one of available choices`, function () {
             randomDecision.getRandomChoice().should.equalOneOf(randomDecision.choices);
         });
@@ -35,4 +35,14 @@ describe('randomDecision', function () {
             should.fail(selectedChoices, expectedChoice, 'Last choice was never selected');
         })
     })
+    describe('#getRandomChoice(seed)', function () {
+        it('should always select the same value when the seed is the same', function () {
+            const seed = new Date();
+            const initialDecision = randomDecision.getRandomChoice(seed);
+            for (let i = 0; i <= 1000; i++) {
+                let randomChoice = randomDecision.getRandomChoice(seed);
+                assert.strictEqual(randomChoice, initialDecision);
+            }
+        })
+    })
 })