What Is The Purpose Of Unit Testing?

Unit Testing| What Is Its Importance In Software Testing?

In the software development process, there are usually cases when a system doesn’t work because of the existence of a small bug. To avoid wasting money and time fixing such errors, developers and QA engineers use unit testing to check the performance of every piece of the software immediately after it is written. Unit testing aims to provide quality assurance that each unit of the software code performs as anticipated. It assists developers in understanding the testing code base and allows them to make changes faster.

Table of contents:

1. What is unit testing?
2. Types of unit testing
3. Unit testing frameworks
4. Advantages of unit testing
5. Unit testing tools: The best unit test frameworks
6. Unit test example: mock objects
7. How to adopt unit testing: best unit testing practices
8. Unit testing versus integration test

What is Unit Testing?

Unit testing is a software testing approach where “units,” the individual software components, are tested. Typically developers write unit tests for their code to ensure that the code works correctly. This is important in detecting and protecting against bugs in the future. Sometimes, developers write unit tests before writing the code. This method is known as TDD (Test-driven development). In the TDD approach, requirements are turned into specific test cases; the application is improved to pass the new tests. Generally, no code is added that hasn’t been proven to meet defined requirements.

TDD and unit testing are similar in that Unit testing allows developers to modify code without impacting the functionality of other units or the product. Unit tests are often written in the form of functions and check the behavior and value of these functions in various situations.  

A unit may be an individual module, object, procedure, method, or function. It is the smallest testable part of any software.  In V Model, STLC, SDLC, Unit testing is the initial level of testing done before integration testing. Typically unit testing is a WhiteBox testing technique that the developer often performs. Even though in a practical world, because of time crunch or reluctance of developers to do tests, QA engineers also do unit testing.

Types of Unit Testing

The main aim of unit testing is to make sure that every individual part is working well and as it is supported to work. The whole system will work well if the individual parts are working well. Generally, there are two main types of testing units:

1. Manual tests
2. Automated tests 

Manual Tests

In manual unit testing, there is a step-by-step instructional procedure that assists testers in performing this task efficiently. However, the automated unit testing approach is preferred as it is faster and more accurate.

Automated Tests

This approach usually entails the developer first writing a section of the code in the application so that the function can be tested.  After that, developers remove the test code when the software is used. Additionally, they can isolate the function to test it more thoroughly. This assists with identifying and dependency that might be there between the tested code and the other data spaces. These dependencies can then be removed. To attain full automation and protect the process from the human factor, programmers deploy specialized frameworks that enable them to embed performance criteria in test conditions and keep error logs. 

Unit Testing Frameworks

The workflow of unit testing in software testing typically follows the framework below:

1. Create the test cases
2. Rework or review
3. Baseline
4. Execute test cases

Generally, unit cases should be independent so that if there are changes needed, they can easily be made without the other ones being impacted. Only one piece of code should be tested at a time, and there should be clear naming conventions to make the process much simpler and clearer. Any bugs identified should be fixed first before proceeding to the next phase.  The unit testing process can be complex or simple, based on the application used and the testing strategies deployed by the developers or the independent testers.

Advantages of Unit Testing 

Some developers underestimate the advantage of writing unit tests. Here are some benefits of unit testing that you should consider before forming your own opinion.

Unit Testing will help you save time and money

The earlier a defect is detected in software, the lower the cost of its correction.  When unit tests are written, numerous bugs are found at the software construction stage, which prevents the transition of these bugs to the next stages, including after the release of the product. This saves the company the costs of fixing the bugs later in the development cycle. It also benefits end-users, who do not have to deal with a buggy product. Additionally, you will hugely benefit from enhanced test time estimation, saving you lots of time and resources. 

Bugs are found easily and quickly on a unit tested

A code covered with tests is more reliable than a code without. If a future change breaks something in the code, developers can identify the cause of the problem right away instead of coming through an unwieldy codebase to find the problem. 

Some best practices suggest that developers first run a group of tears or all unit tests locally to ensure that any coding changes do not disrupt the existing code. Nonetheless, consider the human factor: A developer could forget to run unit tests after making changes and submit potentially non-working code to a common branch. Many businesses apply a continuous development approach to avoid this. Continuous integration tools are deployed to enable developers to run unit tests automatically. Therefore, any unwanted changes in the code are detected by a cold, logical machine. 

The speed of censoring non-working code depends on the tools utilized for continuous integration. Tests can be run immediately in real-time to review changes or set to run either a one-time check at a certain time interval. In simple words, unit tests assist developers in detecting issues immediately, then fixing them faster. With less resources spent finding bugs, the software development team can move on to the next phase of a project. 

Unit Testing provides quick access to code documentation

Unit testing offers documentation of the system that lets developers learn what functionality a unit provides and how to use it. It is very beneficial in the case of changing a developer: any software engineer who wants to know what features and functionalities a module offers and how to use it can take a look at the unit tests to get a general understanding of the module’s interface (API).

Unit Testing is a key part of extreme programming

Unit tests are essential for the Extreme Programming methodology. Extreme programming is fundamentally a test-everything that can possibly break strategy. Writing unit tests with this methodology makes code refactoring and development simpler, creates living documentation and integration easier.

Refactor codes at later stages/dates

Another importance of unit testing in software engineering is that it allows the programmer to refactor code later and ensure that the module still works correctly (i.e., regression testing). The aim is to write test cases for all functions so that whenever code changes cause a fault, it can be quickly fixed.

Reliable and reusable

Within unit tests environments, the individual units of a product become isolated and have their own area of responsibility. That indicates that the code is more reliable- it has been tested in a contained environment- and thus, reusable. Reusable code is clean, efficient, and consistent. 

Unit testing lowers code complexity

Cyclomatic complexity is a quantitative measure you can utilize to understand exactly how sophisticated the program and its code are. Generally, the more paths implied in a single code block, the higher the complexity. Generally, when there is no control flow statement in the source code, the complexity rate stands at one, and with if statements, it gradually rises to two or more. As you can imagine, this is where attaining perfect unit-test coverage becomes a challenging task. The code’s more conditional statements, the more sophisticated the code block is. 

After the creation of unit tests becomes tiresome, it signals that the code might be over-complicated. However, without unit tests objectively answering the question of whether your code works or not, all you have is your own assumption. But with unit tests, you have concrete proof. 

Unit Testing Tools: The Best Unit Test Frameworks

There are many automated unit test software available to help with unit testing. Here are the best unit testing tools: 

• TestNG: TestNG tool is an open source test automation framework exclusively created for the Java programming languages. This framework resembles Junit and NUnit and supports concurrent testing and annotation support. 
• JUnit: An open-source unit testing framework that works effectively for test-driven development. It is exclusively created to support Java Language. This tool is famous for providing an easy approach to writing code. 
• Jtest: Jtest is an IDE plugin with effective open-source frameworks. The effective functionality that can be achieved with this plugin is one-click action for scaling, creating, and maintaining unit tests. 
• NUnit: This unit testing framework is written in C#, which belongs to the xUnit family. NUnit is an open-source tool capable of supporting all serves and NET languages for the same purpose as JUnit.
• EMMA: This is an open-source toolkit for reporting and analyzing code written in Java language. Emma supports coverage types such as line, method, and basic block. The tool is Java-based, without external library dependencies, and can access the source code. 
• HTMLUnit: HTMLUnit is an open-source unit testing framework to support JavaScript. It provides numerous features for the teams like open-source Java library, support for proxy servers, protocols, cookies, etc. 
• PHPUnit: This is a unit testing tool for PHP programmers. Typically, it takes small portions of code which is known as units, and tests each of them separately. Additionally, the tools enable developers to use pre-define assertion methods to assert that a system behaves in a certain way.
• JMockit: This is an open-source unit testing tool. It’s a code coverage tool with path and line metrics. It enables mocking API with recording and verification syntax. This tool provides path coverage, line coverage, and data coverage.  

Those are just a few of the available testing tools. There are many more, especially for Java and C languages, but be sure you will find a unit testing tool for your programming needs despite the language you use.

Unit Test Example: Mock Objects

Unit testing depends on mock objects being developed to test sections of code that are not yet a part of a complete application. Generally, Mock objects fill in for the missing parts of the program.

For instance, you might have a function requiring objects or variables not developed yet. In unit testing, such will be accounted for in the form of mock objects developed exclusively for the aim of the unit testing done on the section of code. 

How To Adopt Unit Testing: Unit Testing Best Practices

Here are significant testing techniques  you should consider to test a unit successfully:

• Always stick to one code unit at a time: When you are testing a unit of code, even though it relates to multiple use cases, unit testers have to test every use case in different test cases. This will effectively complexify the teams to do code refactoring and changes.
• Make sure unit tests are independent of each other: While performing unit testing, ensure that all the unit tests are independent. If you have any dependencies, unit tests can be affected when there are any enhancements or changes. Additionally, it can simplify the test cases to debug and run. Therefore, always ensure that unit test cases are independent. 
• Use AAA for readability: Typically, AAA stands for Arrange, Act, and Assert. This pattern assists in separating what is being tested from the “assert” and “arrange”; therefore lowers the inter-mix of the assertions with the assistance of the’ Act.’ Thus, the test cases are more readable. 
• Make sure you have proper variable naming: One of the best practices is to have the proper naming of variables in unit testing. Thus, avoid deploying magic strings and also follow consistent and clear naming conventions. 
• Fix the bugs before moving to integration testing: Unit testing is the first stage, and it is practiced before moving to the integration testing phase. Therefore, before moving to the next testing level, ensure you fix all the identified bugs in the unit testing phase. 
• Always separate production code and test code: While performing unit testing, ensure that the test code is not used with the source code in your build script. 
• Before fixing a defect, modify or write a test that exposes the defect: Why? First, you will later catch the defect if you do not fix it properly. Second, your test suite is now more extensive. Third, you will probably be too lazy to write the test after you have already fixed the defect.
• Debugging is simple. When a test fails, only the latest modifications need to be debugged. With testing at higher levels, modifications made over the span of several days, weeks, or months need to be scanned.

Unit Testing Vs Integration Test

Integration testing is conducted after unit testing. It is the second software testing phase, where the small modules that are separately tested in the unit testing are combined or integrated to test the functionality of modules when they are together. Nonetheless, to understand these two testing phases more easily, their key differences have been outlined below.

Integration Testing	Unit Testing
Integration testing is conducted after unit testing and before system testing.	It is the first stage of the testing phase in SDLC.
Integration testing concentrates on identifying the bugs raised by integrating different modules.	This approach focuses on testing the functionality of the individual units.
In this approach, different modules are integrated or combined to test if they work together.	In this unit testing practice, the smallest piece of the code is tested.
Integration testing starts with interface specifications.	Unit testing starts with module specification.
Testers perform integration testing.	It is performed by testers or software developers.
Integration testing is a form of black-box testing.	Unit testing is a form of white box testing.
Maintaining the integration test cases is costly.	Maintaining the unit test cases is inexpensive

Table 1: The difference between unit testing and integration testing

Frequently Asked Questions on Unit Testing

When should you do unit testing?

It is vital to practice unit testing at the first stage of the software testing process before planning for integration testing. 

What is security testing? 

In simple words, security testing is a kind of software testing that uncovers vulnerabilities, risks, threats in a software application and protects malicious attacks from intruders. Security tests aim to identify all possible weaknesses and loopholes of the software system which might cause loss of revenue, information, and reputation at the hands of outsiders or employees of the company.

What is progression testing?

Progressive testing is quite functional. In this approach, you test the application with old test data. It is a first test that rolls to a regression test on retesting.

When an application with a hierarchy like a parent-child module is being tested, the related modules must be tested first.

Generally, the progressive approach testing method has three approaches:

• Hybrid approach
• Bottom-up approach
• Top-down approach

What is performance testing?

Performance testing is a non-functional software testing approach that determines how an application’s speed, stability, responsiveness, and scalability hold up under a given workload. It is a vital step in ensuring software quality. Still, sadly, it is usually seen as an afterthought, in isolation, and to start once functional testing is completed, and in most situations, after the code is ready to release. Some of the goals of performance testing include: data transfer velocity, processing speed, evaluating application output, maximum concurrent users, network bandwidth usage, command response times. Workload efficiency and memory utilization.

When should unit testing be performed?

It is vital to practice unit testing at the original stage of the software testing process before planning for the integration testing. 

What is Agile methodology?

Agile methodology is the most crucial approach to project management, which is effectively utilized in the process of software development. This agile approach has been mainly introduced in the field of software development to overcome challenges with earlier waterfall models and to make processes more effective.