Sameeksha Medewar | 28 Jul, 2023

What is Unit Testing? Types, Pros, Cons and Best Tools


Software development is a long and winding road that involves many phases. More often than not, development involves conceptualization and design, coding, testing, and debugging before a product is finally deployed. If you’re a dev or part of a team working on an app or similar product, you probably already know just how important each step of the process can be. 

Testing is a step that should never be skipped during any product’s development process. It’s how you or your team can check whether a software product is defect-free and consistent with relevant requirements. It’s also how developers find out whether their project is performing to expectations and providing users with a satisfactory experience overall.

Unit testing is one way teams can more effectively find defects in their product so they can fix them before launch day. Today, almost every software development company includes unit testing in its software testing cycle to ensure that every unit of the software product is fully functional and performs as expected.

In this article, we’ll answer the question, “what is unit testing in software engineering?” as we talk about the unit testing definition, its importance, its features, and more. We’ll also talk about the advantages and disadvantages of unit testing and discuss some of its best practices in 2024!

What is Unit Testing?

So what is unit testing in software?

Unit testing is at the top of the testing pyramid, meaning it’s the first level of functional testing — the most critical step in developing an error-free software product. The main goal of unit testing is to test each unit or module of the product at the early stage of development to prevent any errors from migrating to the next level.

But now that we’ve answered the question “what is a unit test?’,” chances are you have another question: what exactly is a “unit?”

A unit is the smallest and simplest part of a product that you can test to improve its performance. It can be a method, procedure, object, or module. This test only requires a few inputs and generates a single output.

The responsibility of performing unit tests usually falls on both web developers and quality analysts. They can choose to do the testing manually or automatically with the help of some tools. Nowadays, however, unit testing seems to be automated more often than not.

unit testing advantages

What Does Unit Testing Do?

You may be wondering, “why unit test? What exactly does it do?” Why can’t you just use a more conventional development process where you do all the work and then perform the testing later? If this is how you’d like to do it, you can! However, unit testing can help in a few unique ways.

The unit test methodology can help companies, teams, or individual software developers improve the quality of their code. Additionally, it can help create reusable code modules to make the coding process go more quickly and smoothly. As the process becomes more streamlined, developers may have an easier time creating simpler and clearer documentation. Unit tests may also help ensure that the end product can integrate seamlessly with other technologies and tools if need be.

Unit testing has several functions that can help you improve your software product and its quality. Its functions include:

  • Aiding in creating a foundation for extensive programming thanks to the reliability of unit test frameworks
  • Helping to evaluate each unit of the software product seamlessly
  • Helping to leverage simple testing techniques such as walk-throughs, reviews, and inspection of programming code
  • Ensures adherence to strict test plans for each isolated unit to generate effective results

Again, it’s worth mentioning that properly conducting unit testing will save you the time and money that you would have spent on finding and resolving errors at a later complex stage.

Unit testing can also help you implement a test-driven development strategy where test cases are created first before any coding occurs. If you’d rather use a more traditional ‘code first, test later’ approach, unit testing can still help you check your work for any errors when you’re ready.

How Do Unit Tests Work?

Unit tests work very simply. Unit tests are pieces of code written to check whether a test subject, a specific software product function known also called a unit, is correct. This process may involve checking whether the unit returns an accurate result, performs an expected function, and more.

If the unit test does not receive the expected result, the test is failed. The inverse is also true — if the unit test gets the desired result, the unit passes, and developers can move on to the next steps.

Who Should Create the Unit Test?

We’ve mentioned above that unit testing can fall under the responsibilities of either a developer or a QA analyst. But who should be responsible for creating unit tests?

Common sense says that creating unit tests should be the responsibility of the QA testers. However, unit testing is more frequently considered to be a part of the programming phase. As such, programmers typically tend to be the ones to create the unit tests because they know their code best, making it easier to navigate through the production code. 

There are a few reasons why unit testing is more commonly done by the developers themselves. These reasons include the following:

  • As the programmer, they are more likely to know how to access parts that they can test easily
  • They are also the ideal choice when it comes to mocking objects, especially ones that may not be accessible otherwise
  • If the developers are the ones creating the unit tests, it can save a lot of time in the long run

More than anything, it makes the most sense for developers to handle making unit tests simply because it can save precious time. Saving time when and where you can is critical when you’re under a time crunch or are behind on your schedule.

Although it’s more common for programmers to create the unit tests, there may be some times when other people might come in later in the process. For example, others may help by writing tests to create safeguards as the programmers refactor or continue prod code development.

Importance of Using Unit Testing

Why unit tests? Why are they essential, and why do so many companies use them in their development processes?

When creating any product or software, finding and fixing potential defects in the early stages of the software development cycle (SDLC) is essential. Unit testing helps developers design robust software components while maintaining sound code. In general, the unit testing methodology helps to eliminate any issues in each code unit. 

Unit testing is a foundational check to ensure that the software product meets the specified requirements and behaves as expected. As such, it is an integral part of every agile software development process. For every software build, developers should execute the unit test suite to generate a report specifying the performance of the software’s every aspect. To ensure a quick resolution, the QA team should be notified of every failed test.

When done correctly, unit testing helps companies save time and money. We’ll touch upon some more specific advantages later on in this article.

Unit Testing and Test Driven Development in Python

Features of Good Unit Tests

We’ve answered the question “what are unit tests?” but have yet to delve into what a unit test entails. What is a good unit test, and how does it help identify bugs in a software product? How should developers aim to create their unit tests? Good unit tests should have most, if not all, of the features below:

  • Fast - Large and complex projects require hundreds of unit tests. A good unit test takes very little time to run — it can take as short as a few milliseconds to complete. Sometimes, you need to run a test repeatedly to check if the specific bug has been eliminated or not. Thus, it is vital to create fast unit tests to make the overall process more efficient.
  • Easy Debugging - Each unit test should be clear enough to tell a story about the behavioral aspect of the application, making it easy to understand. Some tests execute successfully when run individually but fail when integrated, indicating a design flaw.
  • Independent and Isolated - Good unit tests are standalone and usually run in isolation. They are also independent of external factors, such as file systems or databases. It’s vital to ensure that any unit tests you create aren’t dependent on other test cases.
  • Self-checking - Unit tests designed to be automated should be capable of detecting whether they are passed or failed automatically without any human intervention.
  • Repeatable - A good unit test should produce the same results each time you execute it. Unit tests need to perform consistently, as they serve as the basis upon which you check your code and its function.

What are the Different Unit Testing Techniques?

As you might imagine, there are a few different techniques that people use when performing unit testing. Each style may be better for certain situations than others, so when deciding which approach to use, you may want to consider carefully. Following are the three unit testing techniques:

1. White Box Testing

White box testing is also sometimes known as glass box testing or transparent testing. In this unit testing technique, the tester already knows the entire internal functionality of the product being tested. Thus, the white box technique enables testers to verify the software product or system’s function, such as its code, infrastructure, and any integration with external systems.

2. Black Box Testing

As you might imagine, black box testing is the opposite of white box. Some people may refer to this technique as “behavioral testing.” Testers are entirely unaware of the product’s internal functionality in this technique. With black box testing, the primary aim is to test the software product’s functionality to see how it behaves while remaining blind to all of the product’s details. Thus, testers don’t know anything about the product’s code structure or implementation.

3. Gray Box Testing

Gray box testing, also known as semi-transparent testing, is a mix of the abovementioned techniques. Testers are given limited working knowledge of the product’s internal workings when using this technique. Gray box testing has a few subtypes, including pattern testing, matrix testing, orthogonal pattern testing, and regression testing.

How is Unit Testing Executed?

It’s not enough to answer the question, “what is software unit testing?” — we must also look at how it’s done.

All unit testing generally follows a similar step-by-step process. In this process, developers create some code with the express purpose of testing a specific function in a software product. The developers can also choose to isolate this function further, allowing them to test it more rigorously. When functions are isolated, tests may reveal any unwanted dependencies between the test subject and other units. They can then eliminate these dependencies.

Developers and QA testers can carry out unit tests either manually or automatically. However, automated unit testing is by far the preferred method by most.

Manual testing may be more tedious and time-consuming. However, if you prefer to carry out your unit testing manually, you can create an instructional document that you can follow step by step.

Coders use Python’s UnitTest framework or other similar frameworks in automated testing. With these tools, they can develop automated unit test cases. 

The process is usually as follows:

  1. A programmer writes code to test a specific function of the software product. Later on, when the production code deploys, they can comment out or completely remove this test code.
  2. Should they choose, the developer can also isolate the test subject (function) in order to test it more thoroughly. During rigorous testing, results may show unwanted dependencies between the test subject and other units in the software product. Once these unnecessary dependencies are revealed, developers can begin working on eliminating them.
  3. The framework will log any failing results when the developers execute automated unit test cases. Frameworks may also flag or report failed cases in summary. Note that if a failure is severe enough, the framework may stop further testing.

Advantages of Unit Testing

  • Exposes all possible defects in the software product at early stages, allowing them to be corrected and eliminated before moving on to the next step
  • Enhances code readability and quality
  • Simplifies documentation and enables code reuse
  • Saves time and money in catching errors quickly that otherwise might move to later project stages
  • Improves deployment speed to speed up project completion and debugging time

Disadvantages of Unit Testing

  • Implementation costs when introducing and implementing new functionalities
  • Hinders prototype development, where the underlying code changes rapidly
  • The tests use the functionality, thus making it harder for the IDEs to see whether the functionality is in use
  • Tests with interdependencies might impact results when an individual codebase is changed

Common Challenges in Unit Testing

Unit testing isn’t always straightforward. Consider the following challenges throughout the testing journey:

  • Labeling: Test labeling is essential for a smooth testing operation. If you forget this vital task, it could lead to great confusion among team members.
  • Understanding the entire code: Developing software requires excessive coding. Getting along with the entire code can be challenging and tedious for the developers, resulting in testing delays.
  • Misunderstanding test doubles: This issue occurs when your mocks are more complicated than the production code. In such a scenario, test doubles help in simplifying tests. The major challenge is when the test double has different names in different books.
  • Debugging: This requires significant time and effort. So, if any tests fail constantly, the consequent debugging will result in more delays.

Unit Testing Best Practices

If you’d like to get better outcomes while conducting your unit tests, you may want to follow some of the best practices for unit testing. Consider the tips below:

  • Make sure all units are independent: Any dependencies will impact the unit tests whenever there is a new change requirement. Also, dependencies increase the complexities while debugging test cases.
  • Test multiple use cases: A single unit relates to several use cases; thus, a tester has to test each use case in different test cases, allowing the teams to refactor or change the code effectively.
  • Use AAA (Arrange, Act, and Assert): This pattern will separate what is being tested from the “arrange” steps, reducing the intermixing of the assertions using “Act” and making the test cases more readable.
  • Label properly and consistently: Always make sure to have proper naming of the variables, test cases, scenarios, etc., to avoid using magic strings for better readability and understanding among teams.

What Do Unit Tests Look Like? A Unit Testing Example

Unit testing follows a specific workflow:

Create the test case(s) → Review → Baseline → Execute the test cases

A unit test can be practically anything you want it to be. It could be a bit of code, a class, or even a method. However, when it comes to unit testing, smaller is always better. Smaller tests will allow you to run your tests faster, and you can also run more of them concurrently.

Here is a great example of a small and simple unit and unit test. It has one class which adds two numbers and a single test function for the class.

public class Adder{

public int addnum(int num1, int num2){

return num1 + num2;



import org.junit.Assert;

import org.junit.Test;

public class Addertest{


public void test addnum(){

Adder adder1 = new Adder();

int num1 = 3;

int num2 = 2;

int result = adder1.addnum(num1, num2);

Assert.assertEquals(5, result);



Best Unit Testing Tools

You don’t have to conduct your unit testing manually (unless you want to). There are plenty of tools available to help you along the way, such as:

1. Jtest


Jtest is an open-source IDE plugin offering one-click actions to create, scale, and maintain unit tests. You can use this tool to automate the critical aspects of unit testing to save time, which allows the team to focus on business logic and create more meaningful test suits.

2. JUnit


JUnit is a free unit testing tool most suitable for Java unit testing. This tool comes with support for the assertions that identify the test method. JUnit first tests the data and then uses the data within the code.

3. NUnit


NUnit is a testing framework that is well-suited for .Net programmers. You can use this open-source tool for writing manual scripts. This tool comes with support for data-driven tests that can run simultaneously.

4. JMockit


JMockit is an open-source code coverage tool for Java. It uses recording and syntax verification for mocking the API and comes with line, path, and data coverage.



This open-source tool can analyze and report written code in Java, similar to JMockit. EMMA also supports the different types of coverage, such as method, line, basic block, and more.

6. PHPUnit


PHPUnit is well-suited for PHP developers. You can use it to test units individually with the help of the pre-defined assertion methods to make sure that the system behaves in a specific manner.

What is Test-Driven Development?

Test-driven development (TDD) is sometimes also referred to as test-first development (TFD). But what is it, exactly? And how does it relate to software unit testing?

TDD is an iterative approach in software development where developers create test cases before writing any production code. In essence, test cases are developed for each functionality before any coding happens. These test cases aim to simplify the development process and minimize bugs and defects in the final product.

Tests are generally simple, containing requirement conditions that production code must be able to meet. Each test case is developed to help specify and then validate what the production code needs to do. Once the test cases are created, production code is written and then checked against these test cases. If the code fails, developers can readjust until the result meets the test case requirements.

There are three phases to TDD, namely:

  1. Creating test cases for verifying the functionalities of each specific feature. Developers must ensure that tests correctly compile to ensure they will execute. The test cases must also be precise.
  2. Performing necessary code corrections is the next step if the test fails. Developers must make the necessary changes to the code until it passes the test. This step can be repeated as many times as needed.
  3. The last step is to refactor the code as needed. Once the code has passed all the tests, developers can then do checks for any code redundancies. Additionally, devs can also make code optimizations to improve performance. However, programmers must do this step carefully to avoid affecting the product’s previously tested function.

Test-driven development comes with a bit of a learning curve but can be a valuable tool in a developer’s arsenal. Done well, it can inspire confidence in the end product. Understandably, not everyone prefers the test-driven approach to development as it may sometimes get tedious.


Unit testing is a type of software testing done during the coding process that helps to identify bugs and issues during the early stages of product development. When done correctly, it can help developers find errors and figure out their root causes. Through successful unit testing, developers can correct their code and make the necessary optimizations before product deployment. Since every unit or component of the software product gets checked in unit testing, it helps to ensure that the result is of high quality.

Ready to learn more about software testing? Check out these software testing tutorials and courses.

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By Sameeksha Medewar

Sameeksha is a freelance content writer for more than half and a year. She has a hunger to explore and learn new things. She possesses a bachelor's degree in Computer Science.

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