test(@angular-devkit/build-angular): add basic serve e2e tests

Author: alan-agius4

tests/legacy-cli/e2e/tests/basic/serve.ts

@@ -0,0 +1,26 @@
+import { request } from '../../utils/http';
+import { killAllProcesses } from '../../utils/process';
+import { ngServe } from '../../utils/project';
+
+export default async function () {
+  try {
+    // Serve works without HMR
+    await ngServe('--no-hmr');
+    await verifyResponse();
+    killAllProcesses();
+
+    // Serve works with HMR
+    await ngServe('--hmr');
+    await verifyResponse();
+  } finally {
+    killAllProcesses();
+  }
+}
+
+async function verifyResponse(): Promise<void> {
+  const response = await request('http://localhost:4200/');
+
+  if (!/<app-root><\/app-root>/.test(response)) {
+    throw new Error('Response does not match expected value.');
+  }
+}