What Is Unit Testing? Types, Tools, and Best Practices


Unit testing is a quality assurance technique where application code is broken down into component building blocks – along with each block or unit’s associated data, usage processes, and functions – to ensure that each block works as expected. This article explains the meaning of unit testing and lists its top tools and best practices for developers. 

What Is Unit Testing? 

Unit testing is defined as a quality assurance technique where application code is broken down into component building blocks – along with each block or unit’s associated data, usage processes, and functions – to ensure that each block works as expected. 

Before any software is developed and released, it must undergo a series of tests to ensure its accuracy and functionality. Software testing begins even before the completion of the application. This way, errors and bugs are detected early before they get lost in various codes.

Generally, every software passes through four stages of testing. The first is unit testing, followed by integration testing, system testing, and finally, acceptance testing. Unit testing forms the foundation on which all other tests are built. Therefore, the accuracy and thoroughness of unit testing are significant factors affecting how well other tests can be carried out and the performance of the software as a whole. 

Understanding the process of unit testing

Unit testing is a process where the minor functional parts of the software are tested individually to ensure the smooth running of the unit. Unit testing is a program testing method used to ascertain individual software components’ functionality, accuracy, and efficiency. These units could be usage procedures, unique functions, modules in a program, etc. 

Unit testing is the first layer of the entire testing process software has to go through before its launch and release. This preliminary testing is often carried out by the team of developers or the software engineer that wrote the code for the software. A higher level of awareness of the intricacies of a program increases the chances of doing a thorough job. Quality assurance engineers are also trained to conduct unit testing.

Unit tests, whether done by the software developer or quality assurance professional, are usually automated, ensuring that a section of the software meets expectations. One can also do unit testing manually. Either way, it is executed during the application or software development stage. 

The primary aim of unit testing is to ensure that a code works as it should, enabling the early detection of potentially fatal errors that can affect the performance of the software. Unit testing is part of Test Driven Development (TDD), a methodology that uses repeated testing to build quality products. Each unit must be independent of any external factor or code in unit testing so testers can clearly interpret the results. 

What is the purpose of unit testing?

Unit testing is a crucial part of software development. Failure to conduct unit tests or doing it with half-hearted measures is likely to create execution problems down the line, costing more time, money, and human resources to fix the problem. The objectives of unit testing include:

  • To verify the accuracy of a section of code
  • To have separate independent sections of a code
  • To locate and address bugs early in software development
  • To Increase the programmer’s understanding of the code base 
  • To be able to effect changes easily
  • To make code reusability more feasible

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Top 8 Tools for Unit Testing 

Globally, the software testing market is expected to grow by $34.49 billion from 2021 to 2025, as per a 2022 report by  Global Market Insights. Unit testing tools form a significant part of this, and your top options are:

1. JUnit

It is a publicly available unit testing framework using Java programming. JUnit was first created in 1997 by two programmers. It has since received frequent version updates. 

JUnit tests data before it is added to the code. With JUnit, you can boost developers’ efficiency, ensure software code consistency, and eliminate time wastage spent in debugging. Apart from offering assertions to test a unit, JUnit is also used to rapidly build codes that can increase the quality of the software’s code. Junit is capable of running test cases within a short time frame.

2. NUnit

NUnit, very similar to JUnit, is also an open-source unit testing tool. The significant difference between it and JUnit is that NUnit was programmed for the .NET framework. It is a prevalent tool and was initially written using the C# programming language. NUnit supports data-driven tests strongly. It also supports the idea of parallel testing using a console runner to load and carry out numerous tests. NUnit uses assertions as an effective method of the asset class. Some of the applications supported by NUnit include silver light, .NET core and Xamarin mobile, etc.

3. DBUnit

DBUnit is an exciting addition to the unit testing process. It was created as a JUnit extension but is also compatible with Ant. DBUnit is especially good for projects with a database, as one of its essential functions is to put the database in a known state between testing periods. Doing this can go a long way in preventing the different issues that may arise out of database disruption after a test. Without restoring the database, subsequent test results might be wrong, whereas there is no actual error in the code. 

Updated DBUnits in streaming mode can effectively work with vast sets of data. DBUnit can also mediate data imports and exports to and from an XML dataset. Lastly, developers can use DBUnits to verify that the data in a database matches the required value set for a given function.

4. HTMLUnit

HTMLUnit is a unit testing tool that exists as an open-source tool written in JAVA. It supports JavaScript and manipulates websites using features like forms, hyperlinks, tables, etc. HTMLUnit allows Java test code to view pages in the different graphical user interface (GUI) formats. It is used to test web applications within JUnit or TestNG environments. HTMLUnit also allows access to the structure and information in received web pages. The testing tool can copy browser behavior in areas such as Transmission Control Protocol (TCP/IP) and HTTP. This way, it can navigate hypertext and retrieve web pages. 

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5. PHPUnit

PHPUnit is a testing tool developed using the PHP programming language in 2001. Like several other unit testing tools, it uses assertions to ensure that the unit of the software being tested gives the expected result. PHPUnit is a part of the xUnit architecture. The tool is hosted on GitHub and can aid developers in finding out hidden problems in newly churned-out codes. It provides logging and code coverage analysis while giving results in different formats like JUnit XML and TestDox. 

6. SimpleTest

Like PHPUnit, SimpleTest is a unit testing tool made with and for the PHP programming language. It is an open-source resource that one can easily use in testing standard but intricate PHP tasks like logging into a site. SimpleTest framework supports SSL, forms, authentication, and proxies. Embedded in the SimpleTest framework is an autorun.php file used to derive executable test scripts from test cases.

7. Embunit

Embunit, meaning embedded unit, is, as the name implies, used for embedded software development. Nevertheless, it is a unit testing tool used by developers and independent testers for software written in C or C++ programming languages. 

With Embunit, the developer is not tied down with writing unit tests but can focus on defining the test behavior. Embunit is structured similarly to JUnit and is made flexible to accommodate any hardware platform. The tool generates final test results in XML format. The desktop version of Embunit is free, but organizations will have to pay for the enterprise version. 

8. ABAP Unit

ABAP Unit is a testing tool used for automatic and manual test processes. It has both a free version as well as a commercial version, just like Embunit. The entire testing process from programming to implementation can be done in ABAP, allowing the user to scrutinize a unit of code for errors. 

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Types of Unit Testing 

There are two ways to go about unit testing – manually performing unit testing or unit tests done by a test automation tool. Let us explore these in detail:

Types of Unit Testing

1. Manual unit testing

Manual testing is unit testing executed without special apps or programs. Every step of the testing process is carried out by individuals (developers or otherwise). Manual unit testing is not frequently seen due to better alternatives and multiple drawbacks. Manual unit testing is cost intensive as workers must be paid for the time expended during the process, especially when it involves non-permanent staff. The process is time-consuming as tests ought to be run each time the code is altered. 

It can also be challenging to isolate and test independent units, making discerning the source of faults elicited during the testing process very difficult. The developer frequently performs manual testing and assesses the software’s stability after adding or removing lines of code. 

2. Automated unit testing 

Automated unit testing is a type of testing that is done without substantial human involvement. The tools used to execute automated tests are ultimately produced by people. However, after creating these tools, the execution is done automatically. Automated tests are conducted as part of the build process of the software. When using the automated unit testing system, the developer writes a section of code in the software to test the function. Developers will eventually remove this code from the entire program just before deployment. 

In addition, automatic unit testing can isolate codes to test them independently by duplicating the code in the test environment. This reveals dependencies between units of code. Automatic testing is largely done using a unit testing tool or framework. There are several unit testing tools available as open source resources. The developer simply codes the criteria into the test and proceeds. The tool also alerts the tester of codes that failed the testing process. 

Automated unit tests can exist as lines of code embedded into the software and should test the smallest possible logic unit. Also, they are expected to run in memory and independent of the available computer network capacity. 

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In addition to these two major types of unit testing, one can implement the following testing techniques during the software development lifecycle:

  • Matrix testing: Matrix testing is a technique used in unit testing that scrutinizes all the variables in a software application. The developer outlines all the technical and business risks while providing a list of variables in the application. The variables are then studied to determine how much risk each represents. Matrix testing can be used to note variables that are not well used or optimized. 
  • Pattern testing: Pattern testing is a technique used in unit testing that tries to identify patterns that lead to errors in software. It uses past incorrect codes or defects to study and draw out a pattern. This helps the developer to know specific details that contributed to errors, how they identified the mistakes and how effective the solution was. All this data can be applied in future cases to identify or correct errors and prevent the development of similar defects in the same software or software programs. 
  • Regression testing: Regression testing is a type of unit software testing used to confirm a code’s authenticity after it has been altered or updated. It checks whether the code change has not affected the program’s features. Simply put, regression testing involves re-executing codes to ensure everything is working as expected. Regression tests are done after bug fixes, updates, or any change has been made to the application. 
  • Branch testing: Branch testing is a type of white box testing technique that aims to verify that every possible branch of a decision point programmed in software is executable. It ensures that each possible branch is executed at least once to detect possible errors before launch. 
  • White box testing: White box testing (also called transparent or glass box testing) is a type of unit testing technique where the test is designed with the internal structure of the software being tested in mind. It prioritizes the process of testing the internal structure of an application. White box testing is used in unit testing but can also be applied to higher levels of software testing. 
  • Black box testing: Black box testing, sometimes referred to as specification-based testing, is a technique used to assess application software’s functionality. It does not deal with the internal structure, so the tester must be ignorant of the inner working of the application before the testing process. 
  • Expression testing: Expression testing is used to check for errors in syntax expressions. Some of these errors include unbalanced parentheses, etc. Expression testing ensures that the program accepts only the correct string of characters in any expression. 

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Best Practices of Unit Testing

After adequately understanding unit tests and what they entail, one can proceed with conducting a unit test. These best practices will come in handy during the process of unit testing:  

1. Write appropriate test names

The essential thing to consider when writing a test is choosing a test name. This is very important because good test names improve the readability of the code both for the programmer and others that may work on that code in the future. There are standard naming conventions that one can apply in unit testing.

2. Create simple tests 

Keeping test codes as simple as possible is key to maintaining correct ones. Unit test codes can also have errors, especially with a high level of complexity. Tests do not need to be fancy. Therefore, features like logic, manual string, or said cyclomatic complexity should be minimal. 

3. Craft deterministic tests

A deterministic test always yields the same result irrespective of the input, as long as the code remains unchanged. This minimizes the incidence of false positives and false negatives. Tests need to be deterministic because a test that presents variable results cannot be trusted. To make a test deterministic, it must be isolated from other test cases, environmental values, and external dependencies. 

4. Address a single use-case

Every test should be used to test a single use case. A particular test program should test a single block of code. This will verify the output and produce better insight into the cause of discovered errors without doubt about where they are coming from.

5. Aim for maximum test coverage 

Developers should completely and thoroughly test a software application as much as possible. However, this is not always feasible due to time and financial requirements. Nonetheless, developers must aim to conduct unit tests for the program as much as possible. 

6. Design unit tests to be as fast as possible

Slow tests are complex for developers to run. They bug down the process and cannot be used frequently. Granted that a test’s speed is subjective and depends on the subject being tested, any test that lasts for over an hour and 15 mins can be classified as slow. 

7. Minimize test dependencies

Tests function best when they do not depend on other software parts. External factors should also not influence the outcome of the test.

8. Adopt test automation 

Although unit tests can be conducted manually, current practices encourage an automated unit testing method. It has proven to be not just efficient and cheaper but also time-saving. Unit testing is an essential function performed by DevOps automation tools that streamline the coding process.

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Even as software development evolves in leaps and bounds, unit testing remains an integral process in the DevOps lifecycle. It helps detect potential errors at the early stages of development. It also ensures that new “good” code is not retrofitted into existing “bad” code units. That is why learning about unit testing and weaving it into your software development pathway is critical. 

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