fix(client) downloaded daily code challenge solution with filename (#64385)

e2e/daily-coding-challenge.spec.ts

@@ -1,4 +1,5 @@
-import { test, expect } from '@playwright/test';
+import { test, expect, type Page } from '@playwright/test';
+import * as fs from 'fs';
 import {
   getTodayUsCentral,
   formatDate,
@@ -65,6 +66,15 @@ const mockApiAllChallenges = [
 
 const mockDaysInMonth = new Date(year, month, 0).getDate();
 
+const runChallengeTest = async (page: Page, isMobile: boolean) => {
+  if (isMobile) {
+    await page.getByRole('tab', { name: 'Console' }).click();
+    await page.getByText('Run').click();
+  } else {
+    await page.getByText('Run the Tests (Ctrl + Enter)').click();
+  }
+};
+
 test.describe('Daily Coding Challenges', () => {
   test('should redirect to archive for invalid date', async ({ page }) => {
     await page.goto('/learn/daily-coding-challenge/invalid-date');
@@ -257,3 +267,33 @@ test.describe('Daily Coding Challenge Archive', () => {
     );
   });
 });
+
+test.describe('Daily code challenge solution can be downloaded', () => {
+  test('Downloaded solution files are named by challenge number', async ({
+    page,
+    isMobile
+  }) => {
+    await page.route(/.*\/daily-coding-challenge\/date\/.*/, async route => {
+      await route.fulfill({
+        status: 200,
+        headers: { 'Content-Type': 'application/json' },
+        json: mockApiChallenge
+      });
+    });
+
+    await page.goto(`/learn/daily-coding-challenge/${todayUsCentral}`);
+    await runChallengeTest(page, isMobile);
+    await expect(page.getByRole('dialog')).toBeVisible({ timeout: 15000 });
+    await expect(
+      page.getByRole('link', { name: 'Download my solution' })
+    ).toBeVisible({ timeout: 15000 });
+    const [download] = await Promise.all([
+      page.waitForEvent('download'),
+      page.getByRole('link', { name: 'Download my solution' }).click()
+    ]);
+    const suggestedFileName = download.suggestedFilename();
+    await download.saveAs(suggestedFileName);
+    expect(fs.existsSync(suggestedFileName)).toBeTruthy();
+    expect(suggestedFileName).toBe('challenge-1.txt');
+  });
+});