build and install an iOS app

Summary:
Allows us to `yarn build ios` the helloworld app.

Changelog: [Internal]

Differential Revision: D57067038

packages/helloworld/__tests__/cli-tests.js

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import {execSync} from 'child_process';
+
+describe('helloworld/cli', () => {
+  it('handles arguments piped as string', () => {
+    expect(
+      execSync('echo "pong=hello" | node ./cli.js ping', {
+        cwd: '../',
+        encoding: 'utf8',
+      }),
+    ).toEqual('Donkey Kong!');
+  });
+});