openApp method
Opens the app specified by appId. If appId is null, then the app under
test is started (using resolvedAppId).
On Android appId is the package name. On iOS appId is the bundle name.
Implementation
Future<void> openApp({String? appId}) {
return platform.action.mobile(
android: () => platform.android.openApp(appId: appId),
ios: () => platform.ios.openApp(appId: appId),
);
}