test(@angular/build): add E2E test for Vitest custom browser configuration

Add an E2E test to verify that the Vitest runner respects the browser configuration defined in `vitest-base.config.ts` when no CLI overrides are present. This ensures that custom configurations, such as specific browser providers or endpoints, are preserved when users rely solely on the configuration file.

Author: clydin

tests/e2e/tests/vitest/browser-custom-config.ts

@@ -0,0 +1,54 @@
+import assert from 'node:assert/strict';
+import { applyVitestBuilder } from '../../utils/vitest';
+import { ng } from '../../utils/process';
+import { installPackage } from '../../utils/packages';
+import { writeFile } from '../../utils/fs';
+
+export default async function (): Promise<void> {
+  await applyVitestBuilder();
+  await installPackage('playwright@1');
+  await installPackage('@vitest/browser-playwright@4');
+  await ng('generate', 'component', 'my-comp');
+
+  // Create vitest-base.config.ts
+  await writeFile(
+    'vitest-base.config.ts',
+    `
+      import { defineConfig } from 'vitest/config';
+      import { playwright } from '@vitest/browser-playwright';
+
+      export default defineConfig({
+        test: {
+          browser: {
+            enabled: true,
+            provider: playwright(),
+            instances: [
+              { browser: 'chromium' },
+            ],
+            headless: true,
+          },
+        },
+      });
+    `,
+  );
+
+  // Create a spec file that asserts browser environment
+  await writeFile(
+    'src/browser.spec.ts',
+    `
+      describe('Browser Environment Check', () => {
+        it('should be running in Chromium', () => {
+          const ua = navigator.userAgent;
+          // Fail the test if it's not Chrome/Chromium
+          if (!ua.includes('Chrome') && !ua.includes('Chromium')) {
+            throw new Error('Expected to be running in Chrome/Chromium, but User Agent is: ' + ua);
+          }
+        });
+      });
+    `,
+  );
+
+  const { stdout } = await ng('test', '--no-watch', '--runner-config');
+
+  assert.match(stdout, /3 passed/, 'Expected 3 tests to pass.');
+}