Importance of Unit Testing in Software Development

Unit testing is a type of software testing that focuses on individual units or components of a software system. The purpose of unit testing is to validate that each unit of the software works as intended and meets the requirements. Unit testing is typically performed by developers, and it is performed early in the development process before the code is integrated and tested as a whole system.

Unit tests are automated and are run each time the code is changed to ensure that new code does not break existing functionality. Unit tests are designed to validate the smallest possible unit of code, such as a function or a method, and test it in isolation from the rest of the system. This allows developers to quickly identify and fix any issues early in the development process, improving the overall quality of the software and reducing the time required for later testing.

Let's look at the major testing types that can be performed on any software:

As you can see above, Unit Testing is the very first step in the Software Testing ladder. But it is also an important phase for developers.

As a developer, you may have dismissed unit testing as a waste of time or a task that takes away from development time. However, it is a crucial tool in software development that ensures code is functioning correctly and catches bugs before they cause significant problems.

Fixing one bug can cause another, making unit testing an effective way to avoid errors. It verifies that individual units or components of the software are working correctly before release.

If you have ever worked on a project without unit tests, you may have experienced the pain of fixing bugs that could have been detected earlier. For instance, suppose we consider an e-commerce application that calculates the total cost of items, taxes, and shipping fees during checkout.

Suppose there is a need to modify tax rates or add new shipping calculations. After making the necessary adjustments, the checkout process appears to work as intended. However, users report issues with the feature in specific scenarios a few days later. You discover a bug in your code after hours of debugging that went unnoticed during development.

Developers are familiar with this situation. Bugs are unavoidable in software development, but unit testing can identify them early in the development process before they reach production.

Unit tests examine small, isolated code pieces known as “units.” They offer a rapid and automated approach to verify that individual components of a system work as intended.

Unit testing is an essential software development practice that identifies issues before they escalate into more significant problems.

Objectives of Unit Testing:

The objectives of Unit Testing are:

1. To isolate a section of code.

2. To verify the correctness of the code.

3. To test every function and procedure.

4. To fix bugs early in the development cycle and to save costs.

5. To help the developers understand the code base and enable them to make changes quickly.

6. To help with code reuse.

Structure of unit test (AAA)

When writing a unit test in any technology, it is ideal to follow the AAA process. The test case should be divided into three parts:

1. Arrange: This involves setting up some initial data or environment that will be tested.

2. Act: This part requires performing an action on the arranged data using the actual functional code. In other words, executing the actual code.

3. Assert: After the action is performed, the assert part verifies that the test case does what it is supposed to do.

Let’s consider a simple example:

// Returns the sum of two numbers

function add(a, b) {
  return a + b
}

// Test case

it('should test sum', () => {
  // Arrange
  const a = 5;
  const b = 4;

  // Act
  const total = add(a, b);
  
  // Assert
  expect(total).toBe(9);
});

In this example, we assigned values to variables a and b called the function add(a, b) to calculate their sum. The result of the function was assigned to the variable named total. We then used the expect matcher to verify that the output of the function met the expected criteria.

This example illustrates how the AAA (Arrange-Act-Assert) pattern can effectively structure unit tests, resulting in clear and organized code that developers can easily understand.

Benefits of unit testing

Unit testing has numerous benefits, some of which include:

1. Catching bugs early: By writing unit tests that cover various scenarios, developers can detect errors in their code before it gets integrated with other components, resulting in a quicker feedback loop and saving time and effort later in the development process.

2. Increased confidence in code changes: Unit tests provide a safety net for code changes. Running unit tests after making code changes ensures that developers do not break existing functionality, giving them the confidence to make changes without worrying about introducing new bugs.

3. Improved code quality: Unit testing enforces developers to write more modular and maintainable code that is easily testable, often resulting in better-designed code with fewer dependencies.

4. Faster debugging: When a test fails, a unit test provides a clear indication of where the problem lies, allowing developers to quickly isolate and fix the issue rather than spending hours or even days trying to reproduce and debug the problem.

5. Reduced cost of bug fixes: With unit testing, fixing bugs early in the development process is much cheaper than fixing them after they have made it into production. Unit tests can catch many of these bugs before they get to production, saving time and money.

6. Documentation: Unit tests can serve as documentation for the code, providing an easy way for developers to understand how the code should behave and what it is supposed to do.

When to write the unit test?

I recommend writing unit test cases from the early stage of the project as it offers many benefits that we discussed earlier. However, this is a debatable topic that may vary from project to project and team to team. Some developers and teams may prefer to write unit tests at later stages of development or when adding new features. Nevertheless, it is crucial to keep in mind that catching bugs earlier makes them easier and cheaper to fix.

Writing unit tests from the beginning can also ensure that the code is modular, maintainable, and easy to understand. While it is ultimately up to the team to decide when and how to write unit tests, including them as part of the development process is always good practice.

It is also necessary to keep the unit tests updated after fixing any issues or implementing new features. Furthermore, any changes made in the codebase must pass the test case.

If your project does not have unit tests, I suggest taking the initiative to start writing them.

It’s better to be late than never.

Tools for testing

If you’re looking for testing tools for popular technologies, here are some options to consider:

• JAVA: JUnit

• PHP: PHPUnit

• .NET: NUnit

• Python: PyTest

• NodeJS: Mocha

• Javascript: Jasmine, Jest

These tools can help you streamline your testing process and ensure that your code is functioning as intended.

Myths about unit tests

There are some misconceptions about unit testing that can hinder developers from taking advantage of its benefits. Let’s debunk these myths:

1. Slowdown Development Process: This is a common myth, but in reality, unit testing can actually save time in the long run by catching issues early in the development process and reducing the need for manual testing.
   

2. Hard to Write: Writing unit tests is a simple process that can be learned by developers of all levels. It can also help improve the overall design of your code, making it easier to maintain and update in the future.
   

3. Time-Consuming: While it may seem time-consuming at first, writing unit tests can save time in the long run by reducing the time spent fixing bugs later in the development process.
   

4. Simple code doesn’t require testing: This is a dangerous myth because even simple code can have bugs. It’s always better to catch them early with unit tests to ensure the reliability and quality of your code.
   

Wrapping Up

Unit testing is an essential technique in software development that can significantly improve the quality, reliability, and maintainability of software applications. By detecting bugs early, improving code quality, facilitating refactoring, enabling continuous integration, and reducing costs and time, it can help you create better software applications that meet your stakeholders' requirements.

Happy testing & Enjoy coding!