Monday, June 17, 2024
No menu items!
    HomeTechnologyUnit Testing in Flutter: From Workflow Essentials to Complex Scenarios

    Unit Testing in Flutter: From Workflow Essentials to Complex Scenarios


    Testing is an essential yet often disliked element of programming. We must master it, so I’ll explore the different methodologies for testing applications built with Flutter. It will involve Unit Testing, Widget Testing, and Integration Testing. Flutter developers will implement the comprehensive library in the follow-up to develop more intricate tests for larger-scale projects.

    According to reports, Flutter has overtaken React Native to become the most widely used framework, with over 14 billion downloads for building mobile applications. By having a singular codebase, all platforms can be supported. Unit tests are implemented to ensure the code is maintainable and free of flaws, errors, and faults. It enables a reliable app to be built before it is made available.

    Unit Testing In Flutter

    Unit testing is a software testing method that focuses on verifying the functioning of separate, isolated components of a program. If these components work correctly alone, they can be expected to deliver the desired result when combined. The developers often automate tests, allowing developers to confirm the involvement and output of different elements quickly.

    In software testing, unit testing is a technique that involves isolating distinct parts or units of code and running tests on them with automatic scripts. These tests are designed to analyze the program’s functionality, logic, or structure, focusing on procedural or object-oriented programming.

    Unit tests are not applicable when a dependency exists between different program parts. These tests are designed to verify the proper functioning of the code and that the program continues to meet quality standards. Through these tests, the behavior of the software is verified by developers isolating particular components and tracking any modifications made to them.

    Code Structure While Unit Testing in Flutter

    Before writing unit tests, it is essential to arrange the codebase to allow simple testing of each aspect of the application. MVC and related patterns typically cause the code to be so encompassed with the view that assessing a single piece of logic requires evaluating the right through the idea as well. It means it is arduous to solely test a fragment of reason and instead test the full view.

    When designing a testing framework, it is essential to avoid importing UI-related packages into the unit test package. The Model-View-View Model (MVVM) architecture is suitable as it separates the business and presentational logic. 

    The MVVM pattern transforms data models into a format suitable for a view, and it also enables the use of mock objects for testing the view model layer without involving the UI. It helps to ensure that the unit tests are solely testing the app logic, which is an optimal outcome for developers.

    You can employ a view model to transform JSON data regarding server-side products into a collection of objects, enabling the list view to show a list of products without worrying about the origin of the data. The operation logic is stored in view models, which are segregated from the views. Segmenting processing logic from the views allows you to concentrate your testing attention on the implementation logic.

    Workflow of Unit Testing

    Unit testing is a form of automated testing where individual units of code (functions, methods, classes, states, etc.) are tested using a set of predefined parameters to ensure their reliability. Here is the workflow of unit testing in Flutter:

    1. Initial Setup: 

    The first step in making our app is to switch out the main. Dart for the provided code and create a file called counter. Dart. Further, the developers go to the test folder and clear all the data inside the widget_test. Dart main function. Here are the steps:

    • Add the unit test or flutter_test dependence.
    • Establish a test file.
    • Construct a class for testing.
    • Write the unit test for our class.
    • Join multiple tests within a group.
    • Run the unit tests.

    2. Add The Test Dependency:

    The Dart library provides the essential components for writing tests and optimizing for all web, server, and Flutter applications. It is the recommended practice when putting together packages to be utilized across various platforms.

    test: <latest_version>

    3. Build the Test File: 

    Create two files: counter. dart and counter_test.dart. The counter. The dart file must be in the lib folder and contains the testing class. The counter_test.dart file must store in the test folder and contains the testing details of developers. It is important to note that test files should always have the _test. Dart extension so the test runner can identify them.



    counter. dart



    4. Build the Test Class:

    The following step is to establish a “unit” to assess. Remember that “unit” is just another expression for a function, method, or class. As an example, form a Counter family inside the lib/counter. Dart document. It is responsible for increasing and decreasing a value that begins at 0.

    class Counter {

    int value = 0; 

    void increment() => value++; 

    void decrement() => value–;

    5. Generate the Test:

    Inside the counter_test.dart file and build the initial unit test. Tests are created using the upper-level test function. You can examine the results quickly by using the upper-level expect function. All the extracted function appears in the test package designed by the developers.

    // Import the test package and Counter class

    import ‘package: test/test.dart’;

    import ‘package:counter_app/counter.dart’;void main() {

    test(‘Counter value should be incremented’, () {

    final counter = Counter(); counter.increment(); expect(counter.value, 1);



    6. Unifying Various Unit Test within a Group:

    In case there are multiple calculations linked, using the group function is efficient in the test package to combine them.

    import ‘package: test/test.dart’;

    import ‘package:counter_app/counter.dart’;void main() {

    group(‘Counter’, () {

    test(‘value should start at 0’, () {

    expect(Counter().value, 0);


    test(‘value should be incremented’, () {

    final counter = Counter(); counter.increment(); expect(counter.value, 1);


    test(‘value should be decremented’, () {

    final counter = Counter(); counter.decrement(); expect(counter.value, -1);




    7. Run the Test:

    Now after writing the initial Test, it’s time to execute it. To complete, you can use the ‘Testing’ tab in Visual Studio Code or press CTRL/CMD + SHIFT + P to open the command palette. After typing ‘Testing,’ it will reveal various testing options; click ‘Debug test’ under test/unit_test.dart. 

    After the developers run the Test, you should see either a checkmark signaling it passed or a cross indicating that it failed. You can jump straight to the error if the cross is revealed to see what went wrong.

    8. Final Finishing:

    It’s your job to go ahead now and apply the same process for decrementing. Use the group () function to create a group with a description of the tasks (e.g. decrementing counter values) and then copy and paste your existing tests inside the process. 

    Developers can then find the group under the Testing tab, and if you click on the small arrow, you can see both tests inside the group.

    9. Widget Test:

    We will set up a two-pronged approach to test our Widget, including a description and a function. We add the necessary Flutter components, flutter_test and material. Dart to the primary file main. Dart. It should include the central () part. 

    Then, we will use the testWidget function to call the WidgetTester tester from the function parameter and use the keyword async. In the Set up step, we’ll create a widget for the Test using `western.pumpWidget(const MyApp());`. 

    To Perform, we press the add button using `tester. Tap ()`, which targets the button with `find.byIcon()`. We then call `tester. Pump ()` to execute the setState. Lastly, we’ll use `expect()` for Test to find a widget with the text “1”.

    Requirement of Unit Test in Flutter:

    Here are some critical requirements of unit Tests in Flutter: 

    • Unit testing allows us to detect mistakes early, saving time and resources.
    • Often, we hesitate to refactor our code without thought because it might disrupt the functioning of the unit. Having unit tests in place provides the assurance necessary to make modifications confidently.
    • Unit testing can be quickly drafted and executed, thereby conserving a great deal of time.
    • By examining the test cases, the developers can understand the unit’s purpose, which facilitates easier maintenance in the long run.
    • Creating testing cases for the unit makes it easier to understand its purpose. It serves as better documentation.
    • Identifying the source of the problem in debugging is relatively easy as we know the areas where the issue is present, allowing us to focus on the particular unit or component causing the bug.


    Flutter’s rise in popularity over the past three years is decelerating. However, Flutter developers shouldn’t worry that the end is near. Connect to Flutter Agency for effective unit testing for your company. 

    With its ease of use and effectiveness, we will likely find ways to address any current issues, such as app size or the lack of third-party resources. It’s almost certain that Flutter will remain a popular choice for developers. This article has introduced unit testing, with easy if done correctly and can be pretty enjoyable. 

    Related articles

    Stay Connected


    Latest posts