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February 25, 2024

Your Guide to the Flutter Framework

Mobile Application Testing

Flutter is the newest framework to make a splash in the world of mobile app development. Here, we dive into the Flutter framework, its benefits and drawbacks, and the different ways to test a Flutter application. 

Read along or skip to the content that interests you the most. 

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What Is the Flutter Framework? 

Flutter is a free and open-source UI framework for creating native mobile applications from Google. Released in 2017, Flutter allows developers to build mobile applications with a single codebase and programming language. This capability makes building both iOS and Android apps simpler and faster. 

The Flutter framework consists of both a software development kit (SDK) and their widget-based UI library. This library consists of various reusable UI elements, such as sliders, buttons, and text inputs. 

Developers building mobile applications with the Flutter framework will do so using a programming language called Dart. With a syntax like JavaScript, Dart is a typed object programming language that focuses on front-end development. 

Although Flutter is less adopted than other popular test automation frameworks, an increasing number of tech companies have started realizing its potential. Some notable Flutter applications include Google Ads, eBay Motors, Philips Hue, and Xianyu from Alibaba.  

Related Reading: How to Do Flutter Integration Testing With Perfecto >>

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Flutter Framework Architecture

Flutter is comprised of three architectural layers. Here is a quick breakdown of each one:

  1. Framework. This is the more “visible” part of Flutter’s technology. As already mentioned, this layer of Flutter’s architecture in based on Dart. The rich set of libraries in this layer can be divided into multiple layers, such as the basic foundational classes, the widget layer, and the rendering layer.
  2. Engine. This layer is written in C/C++. The engine provides a low-level implementation of the Flutter framework, as well as other core APIs, e.g. graphics, accessibility support, text layout, and plugin architecture.
  3. Embedder. The embedded is a platform-specific layer that allows the Flutter app to run on any OS. 
Flutter architecture
Source: Flutter.dev
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Flutter Framework Benefits

Although Flutter is a newer cross-platform framework, more and more companies have chosen Flutter over frameworks such as Xamarin, Cordova, and React Native.  

Some of the top reasons why development teams choose Flutter include: 

  • Increased productivity. Using the same codebase for iOS and Android saves both time and resources. Flutter’s native widgets also minimize time spent on testing by ensuring there is little to no compatibility issues with different OS versions.
  • Easy to learn. Flutter allows developers to build native mobile applications without needing to access OEM widgets or use a lot of code. This, in addition to Flutter’s particularly appealing user interface, makes the mobile app creation process much simpler.  
  • Great performance. Users report that it is difficult to notice the difference between a Flutter app and a native mobile app. Unlike other frameworks, Flutter apps do not need a bridge to interact with native components. Since these bridges typically cause performance issues, this gives Flutter a decided advantage. 
  • Cost-effective. Building iOS and Android apps with the same codebase is essentially building two apps for the price of one. Flutter’s singular codebase speeds up time-to-market while cutting mobile app development costs significantly. 
  • Hot reload. This unique feature allows developers to change the code on emulators, simulators, or real devices, and see results in real-time. The changed code is then reloaded immediately while the app is running. No restart required. Hot reloads make building UIs, adding features, and bug fixing simpler than ever.  
  • Available on different IDEs. Developers are free to choose between Android Studio and VS Code to edit their code on Flutter.  
  • Application rendering. This unique feature allows Flutter to draw and display its own UI components. By not relying on UI components from the target system, Flutter offers an unparalleled level of detail, runtime performance, and control when compared to other frameworks. 
  • Great documentation & community. Flutter has many great resources to answer your questions, thanks to its ample documentation with easy-to-follow use cases. Flutter users also benefit from community hubs like Flutter Community and Flutter Awesome for exchanging ideas.  
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Flutter Framework Drawbacks

While Flutter app development presents a lot of positives, it is also important to consider the lesser aspects of the framework: 

  • Flutter is relatively new. While Flutter offers many plugins and UI components, frameworks like Xamarin and React Native offer a much larger selection. While Flutter will not be the new framework on the block forever, this is the situation now. 
  • Dart is not very popular. While it is a great programming language, developers are often much more likely to consider languages such as Java or Kotlin.  
  • Some components are only available for iOS or Android, but not both. These types of components more often support Android since Flutter comes from Google, and Android developers are typically more interested in Flutter than iOS developers.  
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Types of Automated Flutter Tests

Automated Flutter tests fall into three major categories: 

  • Unit testing 
  • Widget testing 
  • Integration testing 

While unit tests test a single function, class, or method, widget tests (also known as component tests) test a single widget. Unit tests and widget tests make up most Flutter tests, tracked by code coverage. Integration tests test either a large part or the entire application, covering all the important use cases. 

Let us understand the purpose of each type of testing with the following overview: 

Unit Testing 

Unit tests for a Flutter app validate the behavior of a single method, function, or class. In other words, unit tests ensure that the method under test provides the expected result based on a given input. They help users write more testable and maintainable code. 

Users can run automated unit tests through the Flutter plugins for IntelliJ and VSCode. In addition to their support for running tests, IntelliJ and VSCode also provide the fastest feedback loop and allow users to set breakpoints.  

Widget Testing 

Widget tests, also known as component tests in other UI frameworks, verify that the widget’s UI looks and behaves as expected when responding to certain interactions. It is much more comprehensive than a unit test, as it involves multiple classes and requires a test environment that provides the appropriate widget lifecycle context. 

Yet at the same time, the widget’s test environment is a much simpler implementation than a more developed UI system. Flutter users should write widget tests for all common widgets being used for their applications. 

Integration Testing 

Integration tests test either the entire app or a large portion of the app. These tests verify application performance and ensure that all the widgets and services under test work together properly.  

Flutter users perform integration tests on either real devices or virtual devices, such as simulators and emulators. These tests run in two parts: deploying the application under test to the device (real or virtual) and then driving the application from a separate test suite. This checks to make sure that everything is working together as expected.  

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Bottom Line 

The Flutter framework presents exciting opportunities for mobile app developers and businesses alike. Building iOS and Android applications with the same codebase on a highly user-friendly interface makes mobile app development fast and cost-effective.  

Combined with Perfecto, organizations can release high-quality Flutter applications quickly and easily. Learn more about our platform to learn about our Flutter testing capabilities in more detail. 

But wait, there's more! Now users can get the most out of Flutter with Perfecto's newly added integration testing capability. 

With Perfecto, you can enjoy Flutter integration support for both iOS and Android apps. That means testing to your heart’s desire on real devices (with virtual device testing to come) to ensure your app is of the highest quality. Flutter integration testing with Perfecto is a seamless, end-to-end process that allows you to feel confident that what you are building will be up to the task required of it.

See Perfecto in action by trying a free 14-day trial today.


This blog was originally published in 2021 and has since been updated for clarity and accuracy. 

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