PeerPlay
Half your friends probably have iPhones. When you need 12 testers for a Google Play closed test, it's tempting to count them anyway: they have Google accounts, they're happy to help, and the opt-in link opens fine in Safari.
The short answer is that they can join, but they can't test. That gap matters more than it looks.
This guide explains what an iPhone user can do with your closed test invite, why counting them is risky, and where to find testers whose phones can actually run your app.
What an iPhone user can and can't do
The opt-in page for a closed test is a normal web page. Anyone on your email list or in your Google Group can open it on any device, sign in with their Google account and accept the invitation. That part works on an iPhone.
What they can't do is install the app. Your test build is an Android App Bundle delivered through the Google Play Store, and there's no Play Store on iOS. The tester can see the Play listing on the web, but the install button only works for an Android device signed in to the same Google account.
There's also no workaround on the iPhone itself. Android apps don't run on iOS, and sideloading an APK isn't possible there either. If someone tells you they installed your test build on an iPhone, they most likely installed something else, or they're looking at the store page in a browser.
Do they count toward the 12?
Google describes the requirement for new personal developer accounts as at least 12 testers opted in to a closed test for 14 consecutive days. Google doesn't publish exactly how it checks each tester, so I can't promise how an opted-in tester who never installed is treated.
What I can say is that counting them is a bad bet. When you apply for production, Play Console asks about your closed test: how you recruited testers, what they did, what feedback you got and what you changed. A test where several people never opened the app gives you weak answers there, and a production rejection costs you more time than finding a few Android users would have.
There's also a practical problem during the test itself. You can't tell from the outside whether an opted-in tester is using the app, so a few iPhone users can make your list look healthy while the real number of people opening the app is much lower. If one of your Android testers drops out on day 9, you find out late that you never had a real margin.
Ways an iPhone user can still help
Check whether they have any Android device lying around. An old Android phone or an Android tablet with the Play Store works fine, as long as it's signed in with the same Google account they opted in with. Many Chromebooks also run Android apps from the Play Store, though how well your app behaves there depends on the app.
If they don't, ask them to help in other ways: review your store listing and screenshots, or pass the opt-in link to someone they know with an Android phone. That's worth more than an opt-in that never turns into an install.
Check who can actually test before you start
Before you send the opt-in link to anyone, ask one simple question: which phone do you use every day? It takes ten seconds and saves you from planning around testers who can't install anything.
Then ask each Android tester which Google account their Play Store uses. People often have two or three Google accounts, and the one they give you for the email list isn't always the one on their phone. A mismatch looks exactly like the iPhone problem: the tester is on your list, but the Play Store says the app isn't available.
Once the test is running, ask testers to tell you when they've installed and opened the app, and look at your own analytics or crash reporting for new sessions. That's a better signal than the opted-in number alone.
Find testers who are actually on Android
The developers most likely to have Android phones are other Android developers, and they're also the ones who need testers themselves. That's the idea behind a swap: you test their app, they test yours.
I built PeerPlay after running into the 12-tester requirement with my own Android app. Developers test each other's apps in tracked 14-day rounds, and PeerPlay checks that a tester actually opened your app for a real session, not just installed it. Testers who go quiet are removed from the round, so you can replace them before your count drops.
FAQ
Can an iPhone user opt in to a Google Play closed test?
Yes. The opt-in link opens a web page, so they can accept the invitation from Safari with their Google account, as long as that account is on your email list or in your Google Group. They still can't install the app on the iPhone.
Can testers use an Android tablet instead of a phone?
Usually yes, if the tablet has the Google Play Store and is signed in with the same Google account the tester used to opt in. Make sure your app isn't restricted to phones in its device settings, or the tablet won't be able to install it.
Do I need iPhone testers at all for a Google Play app?
No. Google Play closed testing is only about Android. If you also ship on iOS, Apple has its own beta testing through TestFlight, which has different rules and doesn't count toward anything on Google Play.
How many Android testers should I recruit?
More than 12. People drop out, forget, or change phones during two weeks, and the 14 days only count while you have enough opted-in testers. Recruiting 15 to 20 Android users gives you room to lose a few without starting over.