Testing has always been a crucial step in the software development life cycle (SDLC). In the era of AI-assisted development, when AI agents can generate code with less hands-on human involvement, I believe testing is more important than ever. A robust testing methodology, striking the right balance between manual and automated validation, is key. This approach empowers development teams to deliver high-quality source code with confidence and speed.
This article dives into Integration Testing within Flutter, Google's popular cross-platform app development framework, which allows teams to work on multiple apps in a single codebase. In the context of Flutter, integration testing is often synonymous with end-to-end and UI testing. These comprehensive tests are designed to verify the behavior of the entire application when running on actual devices, ensuring that all components work together as intended in real-world scenarios.
Selecting an optimal automated testing framework is crucial for any development project, and Flutter is no exception. While there are several options, each with its own strengths, I'll share my experience with mobile automated testing frameworks for Flutter and why Patrol is the best solution for conducting integration testing for an iOS and Android Flutter app.
Flutter’s Built-in Integration Testing Framework
Flutter provides a built-in integration testing solution through its own “integration_test package.” This package integrates with your cross-platform Flutter project, allowing you to maintain your test suite within the same codebase as your application. It leverages Dart for writing tests, ensuring a consistent and familiar environment for developers.
The integration_test package also provides the benefit of writing a cross-platform Flutter app, allowing you to write one test that can be executed against both iOS and Android platforms. However, there is a catch.
A significant limitation of Flutter's integration_test package is its inability to interact with native views. Native views encompass any UI elements rendered by the device's operating system rather than using Flutter's own rendering engine. This includes system alerts, permission dialogs, webviews, and any other platform-specific UI components. The limitation stems from Flutter's architecture, which uses its own rendering engine and bypasses the native platform's UI components. Flutter's integration_test package can only interact with elements within its own widget tree, leaving it unable to directly manipulate or verify interactions with these crucial system-level interfaces.
As someone with hands-on experience writing integration tests for a production-grade, cross-platform Flutter app, I've encountered this limitation as a significant obstacle. Modern mobile applications for iOS and Android routinely interact with system-level features, which makes this constraint particularly challenging. Common scenarios that highlight this issue include:
- Requesting location or notification permissions during onboarding
- Utilizing a webview for authentication or payment
The Patrol package saves the day when it comes to interacting with native views.
Introducing Patrol: An Open-Source Companion Package for Flutter’s integration_test
Patrol is a powerful, open-source pub.dev package created and supported by LeanCode that builds on top of the flutter_test and integration_test packages. Patrol empowers developers to write comprehensive integration tests that can interact with both Flutter-rendered elements and native user interface components. This capability not only solves the critical limitation of testing native views but also introduces additional benefits that enhance the overall testing experience for those writing Flutter integration tests.
Patrol addresses the challenge of interacting with native views through a sophisticated dual-process approach:
- Flutter Process: The main Flutter app runs as usual when testing.
- Native Instrumentation Process: Patrol initiates a separate, platform-specific process that runs alongside the Flutter app:
- For iOS: Utilizes XCUITest, Apple's native UI testing framework
- For Android: Employs UIAutomator, Google's UI automation framework for Android
Patrol is added to your Flutter project through pub.dev like any standard dependency in your pubspec.yaml file. The package also has a companion CLI that is required for the processes of building and executing tests. Both the Patrol package and companion CLI are actively maintained.
Key Features and Benefits of Patrol
While Patrol's primary strength lies in its solution for interacting with native views, it also offers additional advantages for developers writing integration tests:
- Applying Hot Restart to Tests: Using the Patrol develop command, you can rapidly increase the time it takes to develop and run an integration test by rerunning your test without having to compile again. This works similarly to using Hot Restart (not to be confused with Hot Reload) when developing your UI with Flutter — any changes are reflected in the test after executing a Hot Restart. Check out this video to see the develop command and Hot Restart feature in action.
- Enhanced Flutter Widget Interaction: Patrol extends Flutter's built-in finder system, providing more robust and flexible ways to locate and interact with widgets. In my experience, this is optional. So, if you would like to stick to Flutter's default way of writing finders for your widgets/elements, go for it!
Setting Up Patrol
Setting up Patrol requires configuration at both the Flutter and native levels of your project. This involves modifications to your iOS and Android project folders to enable native automation capabilities. Due to the complexity of integrating with platform-specific testing frameworks, it's recommended to follow Patrol's official documentation for step-by-step instructions on installing the CLI, setting up necessary native configurations in the iOS and Android folders, and verifying the installation.
Patrol’s Limitations and Considerations
I want to note that Patrol is not compatible with all device farms. In Patrol’s documentation, they advertise support for Firebase Test Labs, Browserstack, and LambdaTest. Other device farms may require custom configuration or may not be compatible. As a result, usage of Patrol within your CI/CD pipeline will depend on your setup. If you have control over the execution of your tests (e.g., executing tests directly through GitHub Actions), you should have no problem running tests with Patrol.
It’s also important to be aware of compatibility between the Patrol package and CLI. Certain versions of the package are only compatible with specific versions of the CLI as listed here in the documentation.
Help Patrol Evolve with Your Work
If you run into a problem or see something you want to improve within Patrol, let the world know!
The Patrol repository is open-source and welcomes contributions from the community. I’ve recently made my own contributions to the repository to solve minor issues I’ve run into in the past.
As the landscape of cross-platform mobile app development evolves, so must our testing strategies. That’s the best way to ensure we're delivering high-quality user experiences with confidence and speed. If you’re starting a new Flutter project, explore Patrol to experience how it can elevate your integration testing capabilities and empower you to build more robust and reliable mobile applications.
