fix(api): shuffle generated exam answers each time (#61352)

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>
Co-authored-by: Mrugesh Mohapatra <1884376+raisedadead@users.noreply.github.com>

api/prisma/schema.prisma

@@ -492,28 +492,28 @@ type SurveyResponse {
 // ----------------------
 
 model DailyCodingChallenges {
-  id                String @id @default(auto()) @map("_id") @db.ObjectId
-  challengeNumber   Int
-  date              DateTime
-  title             String
-  description       String
-  javascript        DailyCodingChallengeApiLanguage
-  python            DailyCodingChallengeApiLanguage
+  id              String                          @id @default(auto()) @map("_id") @db.ObjectId
+  challengeNumber Int
+  date            DateTime
+  title           String
+  description     String
+  javascript      DailyCodingChallengeApiLanguage
+  python          DailyCodingChallengeApiLanguage
 }
 
 type DailyCodingChallengeApiLanguage {
-  tests           DailyCodingChallengeApiLanguageTests[]
-  challengeFiles  DailyCodingChallengeApiLanguageChallengeFiles[]
+  tests          DailyCodingChallengeApiLanguageTests[]
+  challengeFiles DailyCodingChallengeApiLanguageChallengeFiles[]
 }
 
 type DailyCodingChallengeApiLanguageTests {
-  text        String
-  testString  String
+  text       String
+  testString String
 }
 
 type DailyCodingChallengeApiLanguageChallengeFiles {
-  contents  String
-  fileKey   String
+  contents String
+  fileKey  String
 }
 
 // ----------------------

api/src/exam-environment/routes/exam-environment.test.ts

@@ -546,6 +546,8 @@ describe('/exam-environment/', () => {
       });
 
       it('should return the user exam with the exam attempt', async () => {
+        // Mock Math.random for `shuffleArray` to be equivalent between `/generated-exam` and `constructUserExam`
+        jest.spyOn(Math, 'random').mockReturnValue(0.123456789);
         const body: Static<typeof examEnvironmentPostExamGeneratedExam.body> = {
           examId: mock.examId
         };
@@ -576,12 +578,9 @@ describe('/exam-environment/', () => {
 
         const userExam = constructUserExam(generatedExam!, mock.exam);
 
-        expect(res).toMatchObject({
-          status: 200,
-          body: {
-            examAttempt,
-            exam: userExam
-          }
+        expect(res.body).toMatchObject({
+          examAttempt,
+          exam: userExam
         });
       });
     });

api/src/exam-environment/utils/exam-environment.test.ts

@@ -13,7 +13,8 @@ import {
   generateExam,
   userAttemptToDatabaseAttemptQuestionSets,
   validateAttempt,
-  compareAnswers
+  compareAnswers,
+  shuffleArray
 } from './exam-environment';
 
 // NOTE: Whilst the tests could be run against a single generation of exam,
@@ -21,9 +22,13 @@ import {
 //       This helps ensure the config/logic is _reasonably_ likely to be able to
 //       generate a valid exam.
 //       Another option is to call `generateExam` hundreds of times in a loop test :shrug:
-describe('Exam Environment', () => {
+describe('Exam Environment mocked Math.random', () => {
+  let spy: jest.SpyInstance;
   beforeAll(() => {
-    jest.spyOn(Math, 'random').mockReturnValue(0.123456789);
+    spy = jest.spyOn(Math, 'random').mockReturnValue(0.123456789);
+  });
+  afterAll(() => {
+    spy.mockRestore();
   });
   describe('checkAttemptAgainstGeneratedExam()', () => {
     it('should return true if all questions are answered', () => {
@@ -84,13 +89,6 @@ describe('Exam Environment', () => {
     });
   });
 
-  describe('constructUserExam()', () => {
-    it('should not provide the answers', () => {
-      const userExam = constructUserExam(generatedExam, exam);
-      expect(userExam).not.toHaveProperty('answers.isCorrect');
-    });
-  });
-
   describe('generateExam()', () => {
     it('should generate a randomized exam without throwing', () => {
       const _randomizedExam = generateExam(exam);
@@ -385,3 +383,28 @@ describe('Exam Environment', () => {
     });
   });
 });
+
+describe('Exam Environment', () => {
+  describe('constructUserExam()', () => {
+    it('should not provide the answers', () => {
+      const userExam = constructUserExam(generatedExam, exam);
+      expect(userExam).not.toHaveProperty('answers.isCorrect');
+    });
+  });
+
+  describe('shuffleArray()', () => {
+    it('reasonably shuffles an array', () => {
+      const unshuff = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+      const shuff = shuffleArray(unshuff);
+
+      expect(shuff).not.toEqual(unshuff);
+    });
+
+    it('does not mutate the input', () => {
+      const unshuff = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+      shuffleArray(unshuff);
+
+      expect(unshuff).toEqual(unshuff);
+    });
+  });
+});

api/src/exam-environment/utils/exam-environment.ts

@@ -82,11 +82,14 @@ export function constructUserExam(
         return answer;
       });
 
+      // NOTE: Shuffling here means when saved attempt is re-fetched, answers will be in different order.
+      const shuffledAnswers = shuffleArray(answers);
+
       return {
         id: examQuestion.id,
         audio: examQuestion.audio,
         text: examQuestion.text,
-        answers
+        answers: shuffledAnswers
       };
     });
 
@@ -731,8 +734,9 @@ function getRandomAnswers(
  *
  * https://bost.ocks.org/mike/shuffle/
  */
-function shuffleArray<T>(array: Array<T>) {
-  let m = array.length;
+export function shuffleArray<T>(array: Array<T>) {
+  const arr = structuredClone(array);
+  let m = arr.length;
   let t;
   let i;
 
@@ -742,12 +746,12 @@ function shuffleArray<T>(array: Array<T>) {
     i = Math.floor(Math.random() * m--);
 
     // And swap it with the current element.
-    t = array[m]!;
-    array[m] = array[i]!;
-    array[i] = t;
+    t = arr[m]!;
+    arr[m] = arr[i]!;
+    arr[i] = t;
   }
 
-  return array;
+  return arr;
 }
 /* eslint-enable jsdoc/require-description-complete-sentence */