The next release of RUnning Girl is scheduled to fall 2017, but the testing start in summer 2017.
The testing of the app, does not require much, just that you use the app, and if you have some issues or idears, you can send feecback to us, then we can fix errors and implement good idears
Apple have an app called Test Flight, that works a little linke the app store.
Here you can get test versions of app, if you have been invited by the Developer, and you will get all the updates on that app.
If there is any purchasing of the app or in the app, none in Running Girls case, the purchase, will look authentic, except for a notification, that your using a Sandbox app store, and therefor, no money is drawing from any account.
here you can sig up as a tester for running girl
When you have been signed up, you will receive an email from Apple, with the invitation as a tester, using TestFlight.
If no test is running at the time you sign up, there might pass some time before you will get the invitation.