Flutter App Development

Unit Testing in Flutter: Best Practices For Building Reliable and Robust Apps

27th Jun 2024

Software development requires unit testing, which is a simple yet essential component. It includes ensuring the proper functionality of an application's most minor components or units, which frequently consist of single functions or code segments.

The minor functional units of your software that can function independently are known as "parts" in unit testing. These might be specific roles or techniques. The final objective is to test each component to ensure they function as intended independently.

Before the software is assembled in its final form, developers can find and address problems by testing each code unit. This proactive strategy prevents minor errors from later growing into significant issues.

This blog aims to provide a comprehensive understanding of Flutter testing so you can immediately implement it in your Flutter App Development services.

What is Unit Testing?

Software tests that focus on testing specific parts of a software product are called unit tests. Software developers and occasionally testers write unit tests while a project is being developed.

Functions, processes, methods, objects, and other elements in an application's source code can all be considered "units" in a unit test. Each development team determines the best unit for comprehending and testing their system. For instance, a class is typically seen as a unit in object-oriented design. Mock objects are used in unit testing to mimic other code segments or connected systems and maintain test simplicity and predictability.

Verifying that each software unit operates as intended and satisfies requirements is the primary objective of unit testing.

How Does Unit Tests Function

Four phases are often included in unit tests:

  • Developers plan and configure the setting, deciding which code units to test and how to run through each unit's pertinent functionality to test it successfully.
  • Developers create the scripts to run the code and build the test cases. They also write the unit test code.
  • Running the unit test and seeing how the code behaves for each test case is the execution of the unit test.
  • By evaluating the outcomes, engineers can find and address any mistakes or problems in the code.

Unit testing is frequently done using test-driven development, or TDD. The developer must write the unit test before the application code is written. That first test will inevitably fail. Until the tests pass, the developer incorporates the necessary functionality into the application. TDD typically produces a stable, high-quality codebase.

Effective unit testing is:

  • Uses "stubs" or "mocks" to imitate external dependencies and executes each test case independently. This guarantees that the unit tests only consider the functionality of the particular unit under test.
  • It focuses on essential components of the unit being tested rather than testing every line of code. In general, unit testing should concentrate on code that impacts the behavior of the software as a whole.
  • Verifies each test case using "assertions" or criteria specified in the code. The testing framework then runs the test and reports failing tests.
  • Runs early in the development lifecycle and regularly.

Developers can be confident that every unit in a software project is practical and error-free when it has undergone extensive unit testing. The next step is to run integration tests to assess the program's major components and their interactions.

The Benefits of Unit Testing

Unit testing involves carefully examining even the most minor components of a program to ensure they function correctly when left alone. This preliminary testing is crucial for multiple reasons.

Early Bug Detection:

Unit testing finds bugs as early in the development cycle as possible. Finding and resolving problems in discrete, tiny units stops little problems from growing into more significant, more intricate flaws that affect the entire system.

Enhancement of Code Quality:

It motivates programmers to create more organized and modular code. Because every unit needs to withstand extensive testing independently, the result is code that is more organized and easier to maintain.

Enables Refactoring:

Developers can refactor code confidently when they have a suite of unit tests. If a modification unintentionally introduces a bug, the current tests quickly identify and fix it.


One helpful type of documentation is unit testing. By demonstrating how each component is meant to function, unit testing simplifies the comprehension of the codebase for new team members.

Techniques for Unit Testing

Structural Unit Testing

A developer creates test cases for structural testing, a type of white box testing, using the internal organization of the code as a guide. The method necessitates figuring out every route via the code. The tester chooses the inputs for the test cases, runs them, and determines the proper result.

The following are the primary methods for structural testing:

  • Testing of statements, branches, and paths: Every program statement, branch, or path is run through a test at least once. The most detailed choice is statement testing.
  • With conditional testing, code depends on value comparisons, allowing developers to choose a test's path.
  • Testing an application against various regular expression values is known as expression testing.

Testing of Functional Units

Functional unit testing is a black-box method for evaluating an application component's functioning.

Principal functional methods consist of the following:

  • Input domain testing involves testing the size and type of input objects and comparing them to equivalency classes.
  • Boundary value analysis tests verify if software reacts appropriately to inputs that exceed boundary values.
  • Syntax-checking tests determine if the program understands input syntax correctly.
  • Equivalent partitioning is a software testing method in which test cases are applied to each data partition created from the input data of a software unit.

Errors-based Techniques

It is ideal for the programmers who created the original code to create error-based unit tests. Methods consist of:

  • Adding known bugs to the code and testing it until they are discovered is known as fault seeding.
  • Mutation testing involves altering specific statements in the source code to test for flaws in the test code. Running mutation tests can be costly, particularly in large-scale applications.
  • Historical test data: Historical data from earlier test case executions is used to determine each test case's priority.

Unit Testing Examples

Android Unit Testing

Unit tests can be executed by developers on PCs or Android smartphones. For Android, there are two primary categories of unit testing.

Any real or virtual Android device can be used to conduct instrumented testing. Together with the application, the developer builds and installs a test version that can read the application's state and inject commands. An instrumented test is a user interface test that opens and interacts with an application.

A brief instrumented test confirms that the code works with a certain framework feature (such as a SQLite database). The developer may run these tests on various devices to evaluate how well the application interfaces with various SQLite versions.

Local unit tests are executed on the development server or PC. Usually, these are quick, little host-side tests that separate the application's test subject from the rest of it. Large-scale local unit testing requires the system to run an Android simulator like Robolectric.

Angular Unit Testing

Angular unit tests separate code fragments to find problems such as errors and faulty reasoning. Running a unit test with Angular for a complex project with poorly segregated components can be difficult. With the aid of Angular, developers may write code that allows for independent testing of each application function.

Async and TestBed are the tools included in Angular's testing package, which is also its primary utility package.

Node.JS Unit Testing

Developers can run JavaScript code on the server side with Node.js. This open-source platform works with well-known JavaScript testing frameworks, such as Mocha. By adding Mocha test API keywords to the code they inject, testers can identify it as test code.

React Native Unit Testing

For JavaScript-based apps, React Native is an open-source framework for developing mobile apps. A Jest testing framework is integrated into it. To make sure their JavaScript codebase is proper, developers can utilize Jest.

The 5 Best Practices For Unit Testing

We have listed the top five unit testing best practices for your application development projects that will assure improved outcomes and profitable and long-lasting testing coverage.

Write reliable, simple unit tests

Establishing a strong unit testing methodology starts with writing dependable unit tests. The test suite must be able to report unexpected or suspicious behavior seen during testing. It shouldn't only state the point at which the test produces the desired result or output.

Unit testing should be automated

Unsatisfactory test results can frequently be caused by manual bias. If flaws are not found on time, they may result in more issues. Avoiding this by requiring automated testing techniques in your technological operations is crucial. Automated unit testing produces far more code coverage, controlled parallel processing of test cases, and faster response. Test engineers can work faster and with less time when they use it.

Prioritize attention to use cases

One key goal of unit testing is ensuring the code is easily maintainable. Furthermore, it guarantees that inexperienced developers can grasp it without any problems. Verifying outcomes versus anticipated results is simpler when one use case is being worked on at a time and the others are prioritized sequentially.

Accelerate tests with improved isolation

Unit tests should be run independently, simulating external dependencies and not relying on other tests. Streamlining and making them stand-alone modules can facilitate faster code coverage, which automation can further enhance. These measures accelerate the test activity, which increases developers' interest in unit testing. If it takes too long, it will be difficult to persuade developers to wait a long time to send their code to the next stage.

Include unit testing in the construction process.

Although Test Driven Development (TDD) developers will offer adequate coverage for unit testing, it is always preferable to incorporate it into the build process for extra security. Unit tests will all be run as part of the build process before moving on to end-to-end test automation. And will additionally inform the relevant parties of any test failure.


Modern application quality assurance strategies will require unit testing as a fundamental component. For many businesses, the challenge will be enabling flawless unit testing implementation. Automating test procedures can be really helpful in this situation. Engaging with a top Flutter App Development Company in India can significantly streamline this process, ensuring robust and efficient testing solutions.

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