What is Unit Testing? - Definition, Pros and Cons, Tools

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What is Unit Testing? - Definition, Pros and Cons, Tools

Sameeksha Medewar
Last updated on May 22, 2024

    Software testing is an integral and indispensable part of the software development life cycle (SDLC). It is a process of verifying that a software product is free from defects, meets quality standards, and complies with the specified requirements. Alternatively, we can define software testing as the process to validate a software product for its correctness, functionality, reliability, and usability. Since the end goal of any organization is customer satisfaction, testing helps them deliver high-quality software products that meet customers’ expectations. Moreover, they carry out a wide variety of testing processes with the goal of delivering a high-quality product. Unit testing is one of the types of software testing. The two broad categories of software testing are functional testing and non-functional testing, and unit testing falls under the category of functional testing. This article will help you know what exactly unit testing is and why it is important? Also, you will learn the significant advantages and disadvantages of unit testing. Finally, you will get familiar with some of the most popular unit testing tools. So, let us start our discussion!

    What is Unit Testing?

    It is a type of software testing that involves testing each unit or component of a software product. Here, the term ‘unit’ refers to the smallest testable part of the software product, such as a function, method, module, object, or procedure, that can accept input and produce output. The primary purpose of unit testing is to ensure that every single unit or component of the software product functions as expected. It is the first level of software testing, followed by integration testing. Generally, developers are responsible for performing unit testing during the development phase, i.e., the coding or implementation phase of SDLC . However, the quality assurance team also sometimes carries out unit testing. Before the software product undergoes integration testing, it evaluates the completeness and correctness of each component or unit in isolation.

    Why Unit Testing?

    It is very significant because it helps to identify flaws and defects in the software product at an early stage of development. Moreover, it helps to detect the part of the code or unit of the software product that has defects or errors, making it easier for developers to resolve them. Many developers carry out minimal unit testing to save time. However, this is not appropriate because improper unit testing may result in high-cost defects fixing during the other levels of software testing, such as integration, system, and acceptance testing. Therefore, it is essential to do proper unit testing in the early development to save time and cost in the later stages.

    Unit Testing Techniques

    We can classify unit testing techniques into three categories, namely white-box, black-box, and gray-box. Let us discuss each of these techniques briefly below.

    • Black-box Testing: This type of testing tests the user interface of the software product, along with input and output.
    • White-Box Testing: White-box testing enables the development team to test the functional behavior of the software product and ensure that it is working as expected.
    • Gray-Box Testing: This type of testing is used to execute test cases, test suites, test methods, and perform risk analysis.

    Code Coverage Techniques in Unit Testing

    Code coverage is a metric in software testing that helps you understand how much of your source code is tested. It is a useful metric for finding the segment of your source code that is not covered by the test suite. The following are some major code coverage techniques employed in unit testing:

    • Statement Coverage: This technique determines the number of executed statements in the source code.

    Statement Coverage = (Number of statements executed) / (Total Number of statements)*100.

    • Branch/Decision Coverage: This technique helps you understand how many branches of the decision control structures, for instance, if statements have been executed in the source code.

    Decision Coverage = (Number of decision/branch outcomes exercised) / (Total number of decision outcomes)*100.

    • Condition/Expression Coverage: This technique determines the number of boolean conditions or expressions executed in the source code.

    Condition Coverage = (Number of executed operands) / (Total Number of Operands)*100.

    Features of Unit Testing

    The following are some salient features of unit testing:

    • It is the first level of software testing and is performed before integration testing .
    • This type of testing is also referred to as component testing.
    • It is a component of test-driven development.
    • There are two ways to perform unit testing, namely automated and manual.
    • It forms the foundation for extreme programming since extreme programming hugely relies on automated unit test frameworks.
    • This type of testing demands strict test plans for each unit to produce effective results.

    Advantages and Disadvantages of Unit Testing

    Let us now gain insights into the significant advantages and disadvantages of unit testing.


    • Unit testing allows developers to test each and every component or module of a software product individually.
    • It highlights all the bugs and errors before the software product undergoes integration testing.
    • It makes the process of debugging easier.
    • In this type of testing, the entire source code is divided into smaller pieces. Such modularity of code makes it more reusable.
    • It significantly reduces the cost of testing by detecting errors and defects in the early stages of development.
    • It becomes easier and safer to refactor code by putting unit tests into place.
    • Each unit or module is independent of the other.


    • We cannot expect unit testing to identify all the errors in the software product. It is not possible for developers with unit testing to analyze and evaluate every execution path of the software product.
    • Since unit testing is intended to identify errors in various units of the software product, it cannot detect broad system-level or integration errors.
    • It is not ideal for testing user interfaces. It works well for testing business logic implementation.
    • This type of testing requires the development team to maintain rigorous discipline throughout the process of unit testing.
    • Writing good quality unit tests is pretty challenging and time-consuming.

    5 Common Challenges of Unit Testing

    While performing unit testing, the development team may encounter certain issues or challenges that may affect the testing process. The following are some common challenges that a development team may face while performing unit testing:

    • Uncertainties with Test Names: There are certain tests whose names do not reflect the aim of the testing. Such test names can create confusion among the team members and can disturb the testing process.
    • Issues with Test Doubles: If the mock code is more complicated and requires more testing than the production code, it is an indicator that there is something wrong with the product. The aim of this mock code is to simplify the testing process.
    • Debugging Tests Frequently: If a specific test fails constantly, it requires frequent testing and debugging. Since debugging is not a simple task, frequent debugging of tests can create a great challenge for the development team.
    • Writing Wrong Type of Tests: This is one of the most common problems when it comes to automated testing. Many times, the development team tends to write a few unit tests and multiple system tests. Therefore, writing wrong tests is one of the biggest challenges in unit testing.
    • Understanding the Entire Code: Reading and understanding the entire source code of a software product is really time-consuming, which may delay the testing process and hence, product release.

    Top 5 Unit Testing Frameworks and Tools

    A plethora of unit testing frameworks and tools are available out there that enable you to perform automated unit testing. Using such frameworks and tools boosts the productivity and efficiency of the testing process. The following are some popular and widespread unit testing frameworks:

    1. JUnit

    JUnit is one of the most widely used unit testing frameworks for the Java programming language. This framework is programmer-friendly and plays a crucial role in test-driven development. It belongs to a family of unit testing frameworks which is known as xUnit. The latest and stable version of JUnit is JUnit 5, which resides under the package org.junit.jupiter. In addition, the primary objective of JUnit 5 is to create an up-to-date foundation for developer-side testing on the Java Virtual Machine (JVM).

    2. NUnit

    NUnit is a unit testing framework for all the .NET languages. This framework is originally ported from JUnit. However, the current and stable version of NUnit, version 3, is completely revised with additional features and support for multifarious .NET frameworks. This framework has a similar purpose as JUnit for Java. In addition, it is one of the frameworks that belong to the family of unit testing frameworks called xUnit. Like JUnit, NUnit is also a significant aspect of test-driven development.

    3. JMockit

    JMockit is an open-source automated testing toolkit for Java. It is a framework for mocking objects in tests developed using Java. It is also a code coverage tool that supports line coverage, path coverage, and data coverage. Moreover, this toolkit supports integration testing for Spring and Java EE-based applications. It can seamlessly integrate with JUnit and TestNG.

    4. EMMA

    EMMA is an open-source code coverage tool for the Java programming language. While supporting large-scale enterprise-level software development, EMMA makes an individual developer’s work fast and iterative. The primary purpose of this tool is for analyzing and reporting source code written in Java. It does not have any external dependencies. Also, it supports various coverage types, including method, line, class, and basic block.

    5. PHPUnit

    PHPUnit is a unit testing framework for the PHP language. Like JUnit and NUnit, PHPUnit also belongs to xUnit. The primary objective of this framework is to make it easier for developers to find mistakes in their newly committed code quickly. Moreover, this framework leverages assertions to ensure that a specific component or unit of a software product behaves as expected.

    Unit Testing Best Practices

    The following are some best practices to follow while performing unit testing to make it more effective:

    • All the unit test cases should be independent. Therefore, any changes in the requirements of the software product should not affect unit test cases.
    • Make sure that the test execution process focuses on only one code at a time.
    • The bugs and errors detected in the software product should be resolved or fixed before moving forward to the next phase of the software testing life cycle .
    • Follow the consistent and precise naming conventions for your unit tests.
    • Write comprehensive and understandable test cases.
    • Make sure to isolate the testing environment from the development environment.
    • Find and use an appropriate testing tool for performing unit testing.
    • Follow the ‘test as you write your code’ approach. Meaning that you should test your code as soon as you write it. If you decide to test code after writing it completely, it may open up more paths for errors.


    This brings us to the end of our discussion on unit testing. The role of unit testing in the software testing life cycle is indispensable. It is the first level of software testing that development teams carry out on a software product to ensure that each unit or module functions as expected. Furthermore, it discovers bugs or defects early in the development process, which saves the cost of addressing bugs in later stages. We hope that this blog post has helped you gain enough clarity on unit testing. Still, if you have any queries regarding this topic, feel free to share them in the comments section below.

    Frequently Asked Questions

    1. Who writes unit tests?

    Software developers are responsible for writing and running unit tests for every single unit of the software product to ensure that it functions correctly. 2. How many levels of testing are there? There are four levels of testing in the software testing life cycle. These four levels of testing are as follows:

    • Unit Testing
    • Integration Testing
    • System Testing
    • Acceptance Testing

    3. What comes after unit testing?

    After unit testing, there comes integration testing, which is the second level of software testing. In integration testing, developers combine all the individually tested units of the software product and test them as a whole. Furthermore, the primary purpose of integration testing is to ensure that there are no defects or bugs after the integration of various units of the software product.

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