[backend][nodejs] Add decision maker with hardcoded decisions A,B,C

backend/nodejs/test/random-decision.js

@@ -0,0 +1,38 @@
+const assert = require('assert');
+const should = require('should');
+const randomDecision = require('../random-decision');
+
+describe('randomDecision', function () {
+    describe('#getRandomChoice', function () {
+        it(`should return one of available choices`, function () {
+            randomDecision.getRandomChoice().should.equalOneOf(randomDecision.choices);
+        });
+
+        it('should return the first choice sometimes', function () {
+            const expectedChoice = randomDecision.choices[0];
+            const selectedChoices = new Set();
+            for (let i = 0; i <= 1000; i++) {
+                const decision = randomDecision.getRandomChoice();
+                selectedChoices.add(decision);
+                if (decision === expectedChoice) {
+                    should.ok(decision, 'First choice was found once');
+                    return;
+                }
+            }
+            should.fail(selectedChoices, expectedChoice, 'First choice was never selected');
+        })
+        it('should return the last choice sometimes', function () {
+            const expectedChoice = randomDecision.choices[randomDecision.choices.length - 1];
+            const selectedChoices = new Set();
+            for (let i = 0; i <= 1000; i++) {
+                const decision = randomDecision.getRandomChoice();
+                selectedChoices.add(decision);
+                if (decision === expectedChoice) {
+                    should.ok(decision, 'Last choice was found once');
+                    return;
+                }
+            }
+            should.fail(selectedChoices, expectedChoice, 'Last choice was never selected');
+        })
+    })
+})