Get started with Game Loop tests for iOS

With Game Loop tests, you can write tests native to your game engine and then run them in Test Lab on devices you choose. This way, you don't need to worry about writing for different UI or testing frameworks. A Game Loop test simulates the actions of a real player, and when you run it on Test Lab, it provides a fast and scalable way to verify that your game performs well for your users.

This page shows you how to run a Game Loop test, then view and manage your test results in the Test Lab page of the Firebase console. You can also further customize your tests with optional features, such as writing custom test results or ending your test early.

What is a Game Loop Test?

A loop is a full or partial run-through of your test on your gaming app. You can run a Game Loop test locally on a simulator or on a set of devices in Test Lab. Game Loop tests can be used to:

  • Run through your game as an end user would play it. You can either script the input of the user, let the user be idle, or replace the user with an AI (for example, if you implemented AI in a car racing game, you can put an AI driver in charge of the user’s input).

  • Run your game at the highest quality setting to find out which devices can support it.

  • Run a technical test, such as compiling multiple shaders, executing them, and checking that the output is as expected.

Step 1: Register Test Lab’s custom URL scheme

First, you must register Firebase Test Lab's custom URL scheme in your app:

  1. In Xcode, select a project target.

  2. Click the Info tab, then add a new URL type.

  3. In the URL Schemes field, enter firebase-game-loop. You can also register the custom URL scheme by adding it to your project’s Info.plist configuration file anywhere within the <dict> tag:


Your app is now configured to run a test using Test Lab.

Step 2 (optional): Configure your app to run multiple loops

If your app has multiple custom URL schemes registered and you plan to run multiple loops (aka scenarios) in your test, you must specify which loops you want to run in your app at launch time.

In your app delegate, override the application(_:open:options:) method:


func application(_app: UIApplication,
                 open url: URL
                 options: [UIApplication.OpenURLOptionsKey : Any] = [:]) -> Bool {
    let components = URLComponents(url: url, resolvingAgainstBaseURL: true)!
    if components.scheme == "firebase-game-loop" {
        // ...Enter Game Loop Test logic to override application(_:open:options:).
    return true


- (BOOL)application:(UIApplication *)app
            openURL:(NSURL *)url
            options:(NSDictionary &lt;UIApplicationOpenURLOptionsKey, id&gt; *)options {
  if ([url.scheme isEqualToString:(@"firebase-game-loop")]) {
      // ...Enter Game Loop Test logic to override application(_:open:options:).

When you run multiple loops in your test, the current loop is passed as a parameter to the URL used to launch the app. You can also obtain the current loop number by parsing the URLComponents object used to fetch the custom URL scheme:


if components.scheme == "firebase-game-loop" {
    // Iterate over all parameters and find the one with the key "scenario".
    let scenarioNum = Int(components.queryItems!.first(where: { $ == "scenario" })!.value!)!
    // ...Write logic specific to the current loop (scenarioNum).


if ([url.scheme isEqualToString:(@"firebase-game-loop")]) {
    // Launch the app as part of a game loop.
    NSURLComponents *components = [NSURLComponents componentsWithURL:url
    for (NSURLQueryItem *item in [components queryItems]) {
        if ([ isEqualToString:@"scenario"]) {
            NSInteger scenarioNum = [item.value integerValue];
            // ...Write logic specific to the current loop (scenarioNum).

Step 3: Create and run a test

After you register Test Lab's custom URL scheme, you can run your test in the Firebase console or with the gcloud beta CLI. If you haven't already, generate an IPA file for your app (you'll need to locate it later).

Run a test in the Firebase console

  1. If you haven't already, open the Firebase console and create a project.

  2. On the Test Lab page of the Firebase console, click Run Your First Test > Run an iOS Game Loop.

  3. In the Upload App section, click Browse, then select your app's IPA file (if you haven’t already, generate an IPA file for your app).

  4. Optional: If you want to run multiple loops (aka scenarios) at a time or select specific loops to run, enter the loop numbers in the Scenarios field.

    For example, when you enter "1-3, 5", Test Lab runs loops 1, 2, 3, and 5. By default (if you don't enter anything in the Scenarios field), Test Lab only runs loop 1.

  5. In the Devices section, select one or more physical devices you want to test your app on, then click Start Tests.

Run a test with the gcloud beta CLI

  1. If you haven't already, configure your local gcloud SDK environment, then make sure to install the gcloud beta component.

  2. Run the gcloud beta firebase test ios run command and use the following flags to configure the run:

Flags for Game Loop tests

Required: Specifies the type of iOS test you want to run. You can enter test types xctest (default) or game-loop.


Required: Absolute path (Google Cloud Storage or filesystem) to your app’s IPA file. This flag is only valid when running Game Loop tests.


The loops (aka scenarios) you want to run in your app. You can enter one loop, a list or loops, or a range of loops. The default loop is 1.

For example, --scenario-numbers=1-3,5 runs loops 1, 2, 3, and 5.


The physical device you want to run your test on (find out which available devices you can use).


The maximum duration you want your test to run. You can enter an integer to represent the duration in seconds, or an integer and enumeration to represent the duration as a longer unit of time.

For example:

  • --timeout=200 forces your test to terminate when it runs up to 200 seconds.
  • --timeout=1h forces your test to terminate when it runs up to an hour.

For example, the following command runs a Game Loop test that executes loops 1, 4, 6, 7, and 8 on an iPhone 8 Plus:

gcloud beta firebase test ios run
 --type game-loop --app path/to/my/App.ipa --scenario-numbers 1,4,6-8

For more information on the gcloud CLI, see the reference documentation.

Run a test locally

To run your test locally, load your gaming app in a simulator and run:

xcrun simctl openurl SIMULATOR_UDID firebase-game-loop://
  • You can find your simulator's UDID by running the instruments -s devices command.

  • If there is only one simulator running, enter the special string "booted" in place of SIMULATOR_UDID.

If your test contains multiple loops, you can specify which loop you want to run by passing the loop number to the scenario flag. Note that you can only run one loop at a time when running your test locally. For example, if you want to run loops 1, 2, and 5, you must run a separate command for each loop:

xcrun simctl openurl SIMULATOR_UDID firebase-game-loop://?scenario=1
xcrun simctl openurl SIMULATOR_UDID firebase-game-loop://?scenario=2
xcrun simctl openurl SIMULATOR_UDID firebase-game-loop://?scenario=5

End a test early

By default, a Game Loop test continues running until it reaches a timeout of five minutes, even when all the loops have been executed. When the timeout is reached, the test ends and cancels any pending loops. You can speed up your test or end it early by calling Test Lab’s custom URL scheme firebase-game-loop-complete in your app’s AppDelegate. For example:


/// End the loop by calling our custom url scheme.
func finishLoop() {
    let url = URL(string: "firebase-game-loop-complete://")!


- (void)finishLoop {
  UIApplication *app = [UIApplication sharedApplication];
  [app openURL:[NSURL URLWithString:@"firebase-game-loop-complete://"]
completionHandler:^(BOOL success) {}];

Your Game Loop test terminates the current loop and executes the next loop. When there are no more loops to run, the test ends.

Write custom test results

You can configure your Game Loop test to write custom test results to your device’s file system. This way, when the test starts running, Test Lab stores the result files in a GameLoopsResults directory on your testing device (which you must create yourself). When the test ends, Test Lab moves all files from the GameLoopResults directory to your project's bucket. Keep the following in mind when setting up your test:

  • All result files are uploaded regardless of file type, size, or quantity.

  • Test Lab doesn’t process your test results until all the loops in your test have finished running, so if your test includes multiple loops that write output, make sure you append them to a unique result file or create a result file for each loop. This way, you can avoid overwriting results from a previous loop.

To set up your test to write custom test results:

  1. In your app's Documents directory, create a directory named GameLoopResults.

  2. From anywhere in your app’s code (e.g., your app delegate), add the following:


    /// Write to a results file.
    func writeResults() {
      let text = "Greetings from game loops!"
      let fileName = "results.txt"
      let fileManager = FileManager.default
      do {
      let docs = try fileManager.url(for: .documentDirectory,
                                     in: .userDomainMask,
                                     appropriateFor: nil,
                                     create: true)
      let resultsDir = docs.appendingPathComponent("GameLoopResults")
      try fileManager.createDirectory(
          at: resultsDir,
          withIntermediateDirectories: true,
          attributes: nil)
      let fileURL = resultsDir.appendingPathComponent(fileName)
      try text.write(to: fileURL, atomically: false, encoding: .utf8)
      } catch {
        // ...Handle error writing to file.


    /// Write to a results file.
    - (void)writeResults:(NSString *)message {
        // Locate and create the results directory (if it doesn't exist already).
        NSFileManager *manager = [NSFileManager defaultManager];
        NSURL* url = [[manager URLsForDirectory:NSDocumentDirectory
                                      inDomains:NSUserDomainMask] lastObject];
        NSURL* resultsDir = [url URLByAppendingPathComponent:@"GameLoopResults"
        [manager createDirectoryAtURL:resultsDir
        // Write the result message to a text file.
        NSURL* resultFile = [resultsDir URLByAppendingPathComponent:@"result.txt"];
        if ([manager fileExistsAtPath:[resultFile path]]) {
            // Append to the existing file
            NSFileHandle *handle = [NSFileHandle fileHandleForWritingToURL:resultFile
            [handle seekToEndOfFile];
            [handle writeData:[message dataUsingEncoding:NSUTF8StringEncoding]];
            [handle closeFile];
        } else {
            // Create and write to the file.
            [message writeToURL:resultFile
                       encoding:NSUTF8StringEncoding error:nil];