The Importance of Unit Testing in Software Development

Unit testing is a crucial part of software testing that is used to test programs and applications to check if they function as per the client’s specifications. It is done during the development or coding phase of the application. A unit in unit tests refers to the smallest individual software component that can be tested. It can be anything- a line of code, a method, a procedure, an object, a module, or a class.

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Alternatively, unit testing involves testing individual components or modules of the software application. The primary purpose of unit testing is to check that all those components are working as intended. The entire system would be able to function properly if all the individual parts are working well.

When performed well, unit tests-

1. Minimize errors and expose them early in the SDLC

2. Increase code readability

3. Improve deployment velocity

4. Enable code reuse

Types of Unit Testing | How to perform Unit Testing?

Unit testing is classified into two types- Manual testing and Automated testing. The manual approach follows a step-by-step instructional document. Though unit testing can be performed manually, it is commonly automated. The automated approach is comparatively faster and more accurate. It involves writing a section of code in the application just to test the function. Developers would later remove the test code when the application is deployed. They could also isolate the function to test it in a more rigorous manner. This helps track down unnecessary dependencies between the tested code and other units or data specs in the application, which can later be eliminated.

Developers, generally, make use of a UnitTest framework to build automated test cases. He/She would then code criteria into the test (using the automation framework) to check for the code’s correctness.

The unit testing workflow goes as follows-

1. Create Test Cases

2. Review / Rework

3. Baseline

4. Execute Test Cases

Unit Testing Techniques

The unit testing techniques are segregated into three types-

1. Black box testing,

2. White box testing, and

3. Gray box testing

Black box testing involves testing the UI along with input and output. Here, testers are not aware of the internal functionality of the system. White box testing focuses on testing the functional behavior of the application, and Gray box testing is used to execute test methods, test cases, test suites, and perform risk analysis.

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The code coverage techniques used in unit testing are Statement Coverage, Decision Coverage, Branch Coverage, Condition Coverage, and Finite State Machine Coverage.

Advantages of Unit Testing

Unit testing offers plenty of advantages, such as-

1. Quality of Code

Unit testing helps identify even the smallest defects that might be present in the units before they are sent further for integration testing, and tends to significantly improve the code quality.

2. Makes the Process Agile

One of the major benefits of unit testing is that it makes the process more agile. When you incorporate new features into any software, you may be required to make changes to the old design and code, which can be a risky and costly affair. By using the unit testing methodology, you not only save time but it also makes the whole process much easier and faster.

3. Easy to Make Changes

When each component of the software is tested individually, updating the system library or refactoring the code becomes very easy. If any problem exists, they are detected in the early phases which enables making changes to the system much easier. Each unit is verified for its accuracy before it is moved to the next phase.

4. Documentation

Unit testing provides documentation of the entire system. Any developer who wants to learn the functionality of a certain application program can learn about the system by going through the documentation of each individual module. It helps them get a brief understanding of the system and understand what each component does.

5. Simplifies the Debugging Process

Unit testing simplifies the debugging process to a significant extent. If any test fails, then only the recent code changes need to be debugged.

6. Reduces Costs

Since the defects are detected in the early stages of the software development life cycle, the cost of fixing the bugs is greatly reduced. These software bugs, if discovered later, can be very expensive to fix.

Unit Testing Best Practices

For an effective and efficient unit testing-

1. Make sure that the unit test cases are independent of each other. In other words, any enhancement or change in requirements should not affect the unit test cases.

2. Stick to testing only one code at a time.

3. Use the AAA pattern for readability where AAA stands for Arrange, Act, and Assert. This helps separate what is being tested from the ‘Arrange’ and ‘Assert’ steps, thereby preventing the inter-mix of the assertions with the help of ‘Act’.

4. Ensure that you follow clear and consistent naming conventions for your unit tests.

5. In case any module undergoes a code change, make sure there is a corresponding unit test case for that module, and the module passes the test before changing the implementation.

6. Before proceeding to the next phase of the SDLC, make sure that all the bugs identified during the unit testing are fixed.

7. While doing unit testing, make sure that the test code is not deployed with the source code in your build script.

Final Thoughts

Unit testing is an indispensable part of software development or software testing. Overlooking unit testing can adversely affect the software application and make the defects more complex to fix at a later stage.

Unit testing can be simple or rather complex depending on the application, testing tools, and strategies used. There are different tools available that would assist you in unit testing such as JUnit, NUnit, PHPUnit, EMMA, and JMockit. There are various other unit testing tools, primarily for C and Java. Just make sure that you pick a tool for your programming needs irrespective of the language you are using.