Imagine building a complex machine, and you want to ensure each tiny part works perfectly before assembling the whole thing. That's exactly what unit testing does in the world of software development.
In this article, we’ll dive into what unit testing is, why it’s essential, and how it can make your code stronger and more reliable.
Unit testing is a software development practice that involves testing individual units or components of a software application in isolation. A unit is the smallest testable part of an application, usually a single function, method, procedure, module, or class.
Together these code units form a complete application, and if they don’t work well individually, they definitely won’t work well together. Unit testing ensures that each component of the software works correctly on its own before integrating it into the larger system.
Unit testing is usually the very first level of testing, done before integration testing. The number of tests to perform in each cycle is huge, but the time it takes for each test is insignificant as these code units are relatively simple. Because of this, developers can quickly perform unit testing themselves.
In certain teams, developers don’t want to allocate their limited bandwidth to do unit testing so that they can focus entirely on development. In these cases, QA engineers will take over unit testing and integrate this activity into their test plan, leveraging the existing testing tools to better execute and manage test results.
Unit testing is crucial to the software testing process for several reasons:
Read More: Unit Testing vs. Functional Testing: A Comparison
1. Test Fixtures
Test fixtures are the components of a unit test responsible for preparing the necessary environment to execute the test case. Also called the “test context,” they create the initial states for the unit under test to ensure a more controlled execution. Test fixture is highly important for automated unit tests because it provides a consistent environment to repeat the testing process.
For example, let’s say we have a blogging application and we want to test the Post Creation module. The test fixtures should include:
2. Test Case
A unit test case is simply a piece of code designed to verify the behavior of another unit of code, ensuring that the unit under test performs as expected and produces the desired results. Developers must also have an assertion to specifically define what those desired results are. For example, here is a unit test case for a function that calculates the sum of two numbers, a and b:
use PHPUnit\Framework\TestCase;
class MathTest extends TestCase
{
public function testSum()
{
// Arrange
$a = 5;
$b = 7;
$expectedResult = 12;
// Act
$result = Math::sum($a, $b);
// Assert
$this->assertEquals($expectedResult, $result);
}
}
The assertion used in this code is $this->assertEquals($expectedResult, $result); verifying that a + b indeed equals the expected result of 12.
3. Test Runner
The test runner is a framework to orchestrate the execution of multiple unit tests and also provide reporting and analysis of test results. It can scan the codebase or directories to file test cases and then execute them. The great thing is that test runners can run tests by priority while also managing the test environment and handling setup/teardown operations. With a test runner, the unit under test can be isolated from external dependencies.
4. Test Data
Test data should be chosen carefully to cover as many scenarios of that unit as possible, ensuring high test coverage. Generally, it is expected to prepare data for:
5. Mocking and Stubbing
Mocking and stubbing are essentially substitutes for real dependencies of the unit under test. In unit testing developers must focus on testing the specific unit in isolation, but in certain scenarios they’ll need two units to perform the test.
For example, we can have a User class that depends on an external EmailSender class to send email notifications. The User class has a method sendWelcomeEmail() which calls the EmailSender to send a welcome email to a newly registered user. To test the sendWelcomeEmail() method in isolation without actually sending emails, we can create a mock object of the EmailSender class. The developer then won’t have to worry if the external unit (the EmailSender) is working well or not. The unit under test is truly tested in isolation.
Read More: Unit Testing vs. Integration Testing: What Are the Key Differences?
Unit tests are generally:
There are several unit testing techniques commonly used to ensure thorough test coverage, including:
1. JUnit
JUnit is an open-source unit testing tool in Java. It does not require the creation of class objects or the definition of the main method to run tests. It has an assertion library for evaluating test results. Annotations in JUnit are used to execute test methods. JUnit is commonly used to run automation suites with multiple test cases.
2. NUnit
NUnit, an open-source unit testing framework based on .NET, inherits many of its features directly from JUnit. Like JUnit, NUnit offers robust support for Test-Driven Development (TDD) and shares similar functionalities. NUnit enables the execution of automated tests in batches through its console runner.
3. TestNG
TestNG, short for Test Next Generation, is a robust framework that offers comprehensive control over the testing and execution of unit test cases. It incorporates features from both JUnit and NUnit, providing support for various test categories such as unit, functional, and integration testing. TestNG stands out as one of the most powerful unit testing tools due to its user-friendly functionalities.
4. PHPUnit
PHPUnit is a programmer-oriented unit testing framework specifically designed for PHP. It adheres to the xUnit architecture commonly utilized by unit testing frameworks such as NUnit and JUnit. PHPUnit operates exclusively through command-line execution and does not have direct compatibility with web browsers.
Test-Driven Development (TDD) and unit testing are two connected practices. The process of TDD involves writing automated unit tests prior to writing the code. These tests will surely fail, since there is no code written yet. After that, they will use the results from these tests to guide their code writing. Once they have developed the feature, they’ll re-execute the previously failed tests to confirm that their code indeed delivers the intended functionality.
TDD is a systematic development approach that consistently offers feedback, facilitating quick bug detection and debugging. Imagine a situation where many frustrated users complain about a major problem that makes the app extremely slow. In an effort to fix this issue, your team quickly releases a patch. Unfortunately, this rushed solution introduces an even bigger problem, resulting in a widespread system failure.
With Test-Driven Development, you can effectively prevent such incidents. Generally, developers that follow the TDD approach will go through a three-step process:
Read More: TDD vs. BDD: A Comparison
Unit testing comes with a host of challenges for developers:
Katalon is a modern, AI-augmented test automation and quality management platform for web, mobile, API, and desktop applications. It provides a unified platform for teams to plan, design, execute, and manage automated testing efforts.
First, let's see how easy it is to create a test with Katalon's Record-and-Playback:
After you've created your tests, you can immediately execute them in the environment of your choice:
Aside from the no-code testing, you also have access to a keyword library that are essentially code snippets to command the system to perform the action you want. For advanced users, there is also the option to switch to scripting in Java and Groovy. You can flexibly switch between these modes and enjoy the best of three worlds!