Sign upSign InSign upSign InSamuel AbadaFollowITNEXT--ListenShareIn the previous part of this article, we touched base on what unit Testing is, how to write unit tests, organizing, running and interpreting unit tests. We also looked at how to write comprehensive unit tests by unit testing a changenotifier with no dependency and another that dependended on a service class. We looked at how to mock dependencies and handle edge cases. Incase you missed it, you can read it here.This article serves as a concluding part to unit testing. In this article, we would look at advanced unit testing techniques, properly mocking dependencies, mocking method channels, handling Code coverage, common mistakes/pitfalls and best practices to effective unit testing.Now, let’s delve into advanced unit testing techniques that enhance the effectiveness of your tests:Test fixtures are a crucial part of unit testing, especially when you need to establish a consistent environment for your tests. They help set up and tear down any necessary resources or data before and after running tests. For example, when testing a database-driven app, fixtures can ensure a known database state before running tests. Let’s explore how to use test fixtures with code examples.In this example, we’ll use the setUp and tearDown functions provided by the test library to create a test fixture.In this example, we create a Database class and use the setUp function to create an instance of the database before each test and the tearDown function to close it after each test. This ensures a clean and consistent environment for each test case. Other functions that could be used for similar operations are setupAll and tearDownAll.In a test group, the setup function is called before each test is run and the tearDown function is called after each test is run. On the other hand, setupAll registers a function to be run once before all tests and tearDownAll registers a function to be run once after all tests.Asynchronous code is common in modern app development. Common asynchronous operations includes network requests or async/await functions. Dart provides built-in support for asynchronous testing using the async and await keywords. Let's look at an example:Code Sample: Testing an Asynchronous FunctionSuppose you have an asynchronous function that fetches data from a remote API:You can write a unit test for this function as follows:In this example, we use the async keyword in the test function and await when calling the fetchData function. This ensures that the test waits for the asynchronous operation to complete before making assertions.Mocking is a technique used to isolate code under test from external dependencies like APIs, databases, or services. The mockito library is a popular choice for creating mock objects in Dart. Another popular library is mocktail which i use alot in my projects. Let's see how to use it:Code Sample: Mocking Dependencies with mockito/mocktailSuppose you have a class that interacts with an external service:You can create a mock version of this class for testing:Using mockito:Using mocktail:In this example, we create a MockApiService using mockitoand mocktail and specify how it should behave when its fetchData method is called in the test. This allows us to isolate our code under test from the actual API service.In a later article in this series, we will deep dive into the world of mocking and faking in testing. We’ll explore how to use libraries like mockito and mocktail , create custom fakes to isolate your code during testing.In Flutter, you often need to interact with platform-specific features using method channels. However, when it comes to unit testing your Dart code that relies on method channels, it’s essential to isolate your tests and avoid executing actual platform-specific code. This is where mocking method channels comes into play.Mocking method channels allows you to simulate the behavior of platform-specific code without making real method channel calls. This isolation is crucial for true unit testing, as it focuses on testing your Dart code in isolation from external dependencies.To mock method channels in your Flutter tests, follow these steps:Note:You need to identify the channel name of the method channel you want to mock, the method which your dart code invokes and the return type of the method.In this example, we set up a mock method channel handler for the my_method_channel channel. We have an arbitrary method fetchDataFromMethodChannel which is basically our dart code/function/method that invokes a method channel. When the Dart code under test invokes the fetchData method on the channel, the mock handler responds with Mocked Data. This allows you to test your Dart code’s behavior when interacting with method channels without executing platform-specific code.These advanced unit testing techniques, including using test fixtures, handling asynchronous code, and mocking dependencies, enhance the effectiveness of your unit tests and ensure that your code is thoroughly tested in various scenarios. Incorporating these techniques into your testing strategy will help you build more reliable and robust applications in the Flutter and Dart ecosystem.Code coverage is a crucial metric in the world of software testing. It measures the percentage of your codebase that is exercised by your unit tests. In other words, it answers the question, “How much of my code is being tested?”To measure code coverage in Dart, we can use tools like the coverage package. This tool helps you analyze your test suite's effectiveness by providing insights into which parts of your code are covered by tests and which are not.Here’s how you can set up in your Flutter project:This command will run your tests and collect coverage data.Generate a coverage report in human readable form by doing the following:View the coverage report by opening the generated coverage/html/index.html file in your web browser. This report provides detailed information about which lines of code are covered by tests and which are not.Code coverage is not just a vanity metric; it’s a valuable tool for assessing the thoroughness of your tests and the overall quality of your code. Here’s why code coverage is important:Code coverage measures the extent to which your code is executed by your unit tests, but it doesn’t guarantee the correctness of those tests. Even if your tests achieve high code coverage, it’s possible that they might not catch all possible edge cases or functional issues.Unit testing is a powerful technique for ensuring the reliability of your code, but like any other skill, it’s easy to fall into common traps and pitfalls. Here are some of the most frequent mistakes developers make in unit testing, along with guidance on how to avoid them:One of the most common mistakes in unit testing is writing tests that are tightly coupled to the implementation details of the code being tested. This can lead to fragile tests that break every time you make a small change in the implementation. To avoid this pitfall:Another common mistake is neglecting edge cases and boundary conditions in your tests. These are the scenarios where your code is most likely to fail, so it’s crucial to test them thoroughly. To avoid this pitfall:Readable and maintainable tests are essential for long-term success in unit testing. Writing tests that are hard to understand or fragile (i.e., prone to frequent breakage) can lead to frustration and decreased confidence in your test suite. To avoid this pitfall:Many developers focus solely on testing the “happy path” of their code and neglect error handling and exception scenarios. This oversight can result in unhandled exceptions and unexpected application behavior. To avoid this pitfall:Unit tests are not static artifacts; they need to evolve alongside your codebase. Failing to maintain and update your tests as your code changes can lead to outdated and inaccurate tests. To avoid this pitfall:Unit tests should be isolated, meaning they should not rely on external dependencies or resources that are not under your control. Ignoring this principle can lead to flaky tests and difficulty in identifying the source of failures. To avoid this pitfall:Writing effective unit tests requires adopting best practices:In conclusion, unit testing is a critical component of software development that enables you to catch bugs early, improve code quality, and confidently refactor your code. In the world of Flutter and Dart, unit testing is essential for building reliable and robust applications.In the next article of our comprehensive testing series, we will explore “Mocks and Fakes in Testing,” delving into the world of isolating code for effective testing. Stay tuned for more insights and practical examples on your journey to becoming a proficient tester in Flutter and Dart.----ITNEXTMobile Engineer | Technical Writer | SpeakerSamuel AbadainITNEXT--6Mahdi MallakiinITNEXT--6Jacob FerusinITNEXT--8Samuel AbadainITNEXT--1John Wogu--Abdelrahman Shehata--Shree Bhagwat--thejufo--Chahat Gupta--5Vovaklh--3HelpStatusAboutCareersBlogPrivacyTermsText to speechTeams