test(seed): Add Test for Unique Challenge Titles (#17035)

Due to the recent problem with two challenges having the same title, I
added a check for unique titles to the test suite so that hopefully
won't happen again.

Addresses a comment in issue #16906, which was recently closed.

BREAKING CHANGE: None

Closes #16906

challengeTitles.js

@@ -0,0 +1,26 @@
+import _ from 'lodash';
+
+class ChallengeTitles {
+  constructor() {
+    this.knownTitles = [];
+  }
+  check(title) {
+    if (typeof title !== 'string') {
+      throw new Error(`Expected a valid string for ${title}, got ${typeof title}`);
+    } else if (title.length === 0) {
+      throw new Error(`Expected a title length greater than 0`);
+    }
+    const titleToCheck = title.toLowerCase().replace(/\s+/g, '');
+    const titleIndex = _.findIndex(this.knownTitles, existing => titleToCheck === existing);
+    if (titleIndex !== -1) {
+      throw new Error(`
+    All challenges must have a unique title.
+
+    The title ${title} is already assigned
+    `);
+    }
+    this.knownTitles = [ ...this.knownTitles, titleToCheck ];
+  }
+}
+
+export default ChallengeTitles;

test-challenges.js

@@ -6,9 +6,11 @@ import tape from 'tape';
 import getChallenges from './getChallenges';
 import { modern } from '../common/app/utils/challengeTypes';
 import MongoIds from './mongoIds';
+import ChallengeTitles from './challengeTitles';
 import addAssertsToTapTest from './addAssertsToTapTest';
 
 let mongoIds = new MongoIds();
+let challengeTitles = new ChallengeTitles();
 
 function evaluateTest(solution, assert,
   react, redux, reactRedux,
@@ -115,6 +117,7 @@ function createTest({
   reactRedux = false
 }) {
   mongoIds.check(id, title);
+  challengeTitles.check(title);
 
   solutions = solutions.filter(solution => !!solution);
   tests = tests.filter(test => !!test);