A Complete Guide To Flutter Testing

What is Flutter?

Flutter is an open-source framework developed by Google to ease out the process of mobile app development and facilitate the code reuse policy. Flutter follows a write-once, run-anywhere model. Therefore, a single code unit can be compiled for various platforms such as Android, iOS, web, Linux, Windows, and macOS.

Also, read - Cross Browser Testing Strategy Explained in Three Easy Steps

Flutter seems to be a great fan of widget-based development. It provides reusable code elements such as buttons and sliders for easy customizations according to the project needs. The second pillar of the Flutter framework is the SDK (Software Development Kit) that helps compile the code according to the operating system such as Android and iOS. Along with these two explicit and solid strengths, all the related features, such as time-saving, cost-cutting, come into the picture.

A case study on Flutter

In this tutorial on Flutter testing, the above-mentioned points seem good in theory, but I am sure they are not as exciting to read as Flutter is in reality. Therefore, I think a short case study on the framework would help you refine the image of Flutter in your mind and analyze how powerful it is.

This case study is about Google Pay, a Google application designed to manage and make payments to other users. The application’s codebase was documented to be 1.7 million lines of code before Flutter. With an application having two separate versions for both the operating systems, the engineer’s time was the major factor for the company. A growing application would soon add more and more features that could increase the complexity of the code. The application did not look sustainable at this point. The idea was suggested to move to Flutter initially as an experiment.

The proposal was initiated to develop the Add-to-app with Flutter. But soon, this proposal turned towards rewriting the complete code and moving to Flutter completely. Of course, betting on such a decision would be highly costly, but considering future developments and how fast Flutter apps are going ahead seemed practical and efficient.

This did not come as a smooth road either. Rewriting an application that itself is constantly updated in original languages and framework costs a lot of money and time. Furthermore, because the app has been re-written and is now essentially a new software with the previous name, you will need to obtain all security reviews and audits for the same app again. However, Google engineers bet that developing a single code copy would be only 1.2 times the work currently two times.

Soon, engineers closed the gap between legacy app maintenance & development. The new Flutter app had all the 300 features and then proceeded to beta-test it in India for 100 million users. The result of all the effort was a smaller-sized application with only 1.1 million lines of code (35% smaller, per the Flutter Google Pay case study) and blazing fast in operation.

It is true that Google has enough money to try something and fail with no impact on their business. But taking such a risk with Flutter only shows how effective the development in this framework is. So for us, it is worth considering before starting any project.

In the next section of this Flutter testing tutorial, we will see the importance of using Flutter before getting into Flutter testing.

Why Flutter Testing is Important

For high-quality, scalable Flutter apps, testing is one key critical area. Most teams and developers have a strong understanding of the importance of testing but often lack the experience of writing good tests, when to write, and where to write.

A good testing strategy helps ensure that current expectations and assumptions are met and increases confidence in the product.

With so many products using flutter, testing is even more crucial to ensure that the code we write now will still function properly no matter how many features we add or how many developers we onboard to the project.

Top products using Flutter

Flutter has been used by a lot of top companies (including Google as mentioned) to develop a fast cross-platform mobile application. Therefore, the top three products are hereby mentioned for Flutter users (or learners) to look around the design style for inspiration, thus making Flutter testing a must.

Reflectly

Reflectly is a journal application that runs artificial intelligence to deal with the negative thoughts and emotions of the user.

Groupon

Groupon helps in connecting users to local merchants for activities, goods, travel, etc. Groupon uses Flutter in its merchant app.

The New York Times

The new york times is a news-related application bringing news from all over the world in different sectors.

The above example shows the usage of Flutter across different domains, thus making Flutter testing absolutely necessary. However, the kind of tests you write for Flutter apps depends on your unique development workflow and needs, but here are some of the most common kinds of tests to get you started:

• Unit - Testing contract and business logic
• Widget - Testing UI separately
• Integration - Testing whether business logic breaks when units work together
• End-to-End - Testing to verify end-user experience
• Golden - Comparing widget screenshots against approved baseline images

How to test Flutter applications

By now, we are convinced that Flutter applications are easy to develop, and with the benefits it offers, it is always on the shortlist before starting a new project. But is it the same case with Flutter testing based on apps?

In Flutter testing, we have two methods:

• Manual testing for things such as user interface, experience, widget compositions, etc.
• Automation testing for verifying the functionality using various types of data and actions on the applications. If you are looking for a cloud-based solution, TestMu AI can serve both purposes on a single platform which is always recommended to work swiftly.

Flutter Testing manually on Real device cloud

Real device cloud could arguably be considered as one of the best choices for mobile app testing as compared to testing on emulators and simulators. It does not cost as much as building a new real device lab and gives us accurate results for the tests. Cloud-based applications host an array of emulators for mobile apps but as a tester, try to prefer real device cloud (I mean, why not!!) if the charges are nominal.

TestMu AI provides an online device farm with 10,000+ real devices over the cloud with an easy-to-use interface, which speeds up the app and web testing process. It provides features such as network throttling, detailed reporting, screenshot testing, and session recording, just to name a few. Testing an application is an easy step in TestMu AI.

• Login to the TestMu AI platform.
• Move to the “Real Device” section.

• Select “Real Time” from the options visible.
• A new panel will open up requesting the application binary from the tester. For convenience and trial purposes, a sample application will already be loaded into the system. We will use the same application here. If you have a binary already with you, you can upload the same.
• Select the device and OS version to run the application on.

• Here, I have chosen iPhone OS and iPhone 11 as the device. Press START once done.

The application will start running on a real chosen device.

You can now interact in real time with your application and start Flutter testing right away. Of course, the same process can be used for automated browser testing but since we are talking about Flutter, let’s stick with app testing.

However, if you want to perform Flutter testing on Android emulator online or iOS Simulators, you can also do that by going to the Real Time Testing option and choosing the App Testing feature.

Here’s the short video on how to perform native mobile app testing on the TestMu AI platform:

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Flutter Testing using FlutterDriver

Flutter testing is fairly easy to implement, especially when using the FlutterDriver extension. FlutterDriver is an extension provided by the flutter_driver package for integration testing Flutter apps on real devices and emulators.

For new projects, Flutter now recommends the integration_test package instead, and publishes a flutter_driver to integration_test migration guide. Tests use the same tester API as widget tests and run with flutter test integration_test.

By using the Flutter Driver extension, we can run tests written in Dart and get results in a machine-readable format. Flutter Driver connects to an application and drives it like a user would, interacting with the widgets inside of it. This allows us to test our applications thoroughly, including edge cases that may be difficult to reach by hand. Unit and widget tests use the flutter_test package, and integration tests now use the integration_test package, which replaces Flutter Driver for new projects.

Flutter Driver is similar to Selenium WebDriver. It is used to automate the Flutter UI and run it against real devices or emulators. The advantage of using Flutter Driver is that we can automate our testing using a specific platform like Android Studio or through the command line.

Flutter Testing using Automation on Real device cloud

For automation testers using Appium as a go-to test automation platform is a good choice. The problem is just the device cloud that they need to have and maintain in-house for such a marathon. Real device cloud supporting Appium can be a feasible choice that can wrap up your app test automation faster than you can expect.

TestMu AI automation provides an Appium Grid for mobile testing with real devices at their end. This way, you can run tests in parallel and integrate CI/CD technologies on the same pipeline. Furthermore, covering all tests in a single place gives you organized and maintained test data and results for better analysis. For trials, you can explore a free plan that includes 100 lifetime automation minutes.

Looking to automate mobile apps on real devices, check out our video below.

Key Takeaway: Flutter apps can be tested manually on a real device cloud or automated with Appium on real devices, while in-code integration tests for new projects should use integration_test rather than flutter_driver.