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What Is Unit Testing? Everything That You Need To Know About Unit Testing

Published on May 22,2019

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The prime objective of any software project is to get a high-quality output while reducing the cost and the time required for completing the project. To achieve that companies subject software product to mainly four levels of testing. Unit testing is the first level of testing in Software Testing. Throughout this article, we will explore what unit test is in detail. If you are new to software testing, be sure to also read the Beginners’ Guide for Software Testing.

Let’s take a look at topics covered in this article:

Levels of Software Testing

Software Testing is a phase within the software development cycle in which business-critical software is verified for correctness, quality, and performance.

There are four fundamental levels within software testing, each examining the software functionality from a unique vantage point within the development process. The four levels of software testing are as shown in the image below.

Levels of Software Testing - What is Unit Testing? - Edureka

This article explains unit testing, the first level of software testing in detail.

What is Unit Testing?

Unit testing is a way of testing the smallest piece of code referred to as a unit that can be logically isolated in a system. It is mainly focused on the functional correctness of standalone modules.

A unit can be almost anything you want it to be – a specific piece of functionality, a program, or a particular method within the application. Smaller the unit, better it is. Smaller tests usually give you a much more granular view of your production, the code is performing. Also, your tests can run faster if they are small. So, it is also micro-level of software testing.

How Do You Perform Unit Testing?

The goal of unit testing to separate each part of the program and test that the individual parts are working correctly and as intended. While performing unit tests, application code functions are executed in a test environment with sample input. The output obtained is then compared with the expected output for that input. If they match the test passes. If not it is a failure. Unit tests are great for confirming the correctness of the code. Let’s take a look at a sample algorithm that illustrates the concept. 

Unit Testing Algorithm - What is Unit Testing? - Edureka

As you can see, performing the unit test is quite simple. You write part of the code and subject it to test. If the test passes then you add it to your test suite and test the next part of the code. Else, you make the necessary changes and retest it again. Repeat the process until all the units of software are tested. This type of basic testing offers a lot of advantages like finding software bugs early, simplifying integration, providing a source of documentation, and many others.

What are the Benefits of Unit Testing?

Conducting regression tests, benefits companies in a number of ways such as:

Makes Coding Agile

Unit testing speeds up the coding process. When you add new features to your application, sometimes you might have to modify the design and code of your software product. However, changing already tested code costs too much money and effort. But with unit tests, you can just test the newly added piece of code instead of testing the entire program. Also, unit tests improve the quality of your code.

Helps Find Software Bugs Early

As unit tests are carried out by developers who test individual code before integration, issues can be found very early in the software testing process. They can be resolved then and there without impacting the other pieces of the code. The advantage of detecting errors early is that you can minimize development risks, and avoid spending too much money and time.

Provides Documentation

In testing, code documentation is often neglected since it requires a lot of time. But unit testing makes documentation a little easier by encouraging better coding practices and also leaving behind pieces of code that describe what your product is doing.

Debugging is Made Easier

Unit testing simplifies the debugging process. When a test fails, only the latest changes made in the code need to be debugged. At higher levels of testing changes made over the span of several days or weeks or months need to be scanned.

Reduces Testing Costs

Since the bugs are found early, the cost of bug fixes is reduced up to some extent. It would cost much more if a bug is found during the later stages of development. You will have to modify the entire code of your project. That sounds really tiring and waste of money. So performing unit testing saves precious time and money as well.

There you go! I hope you are convinced as to why unit testing is important. Moving further, let’s check out a simple demo on how to write unit tests.

Demo: Writing a Sample Unit Test

Unit testing demands that a good test should be:

  • Easy to write
  • Readable
  • Reliable
  • Faster & Efficient

Requirements for the demo:

  • Java Development Kit(JDK)
  • An IDE(In this demo Eclipse is used)
  • Unit testing framework(In this demo TestNG is used)

Let’s get started with the demo. So, in this demo, I have two files:

  • A Math class with a function to test
  • A Test class with methods to perform testing

Take a look at the below code to understand the test case. It’s a Math class with two methods: add, multiply. 

public final class Math {

public static int add(int first, int second) 

  return first + second;

public static int multiply(int multiplicand, int multiplier) 

  return multiplicand * multiplier;


Next up we have a Test class with methods to test the functionality of the add() function and multiply() function.

import org.testng.annotations.Test;

import static org.testng.Assert.assertEquals;

public class MathTests {

public void add_TwoPlusTwo_ReturnsFour() {
final int expected = -4;

final int actual = Math.add(-2,-3);

assertEquals(actual, expected);
public void multiple_twonumbers_retursvalue() {
final int expected = -4;

final int actual = Math.multiply(2,2);
assertEquals(actual, expected);



Unit Test: Checking functionality of add function

Comment the multiply() function in Math class and multiple_twonumbers_retursvalue() function in Test class. Then assign value for the expected variable and call the multiply() function with sample input(consider both positive & negative cases). When you run the test, the expected value is compared with the actual value. If the test is returning the intended results, it means that add() function is working perfectly. I have attached a screenshot of test results when the expected value is -5 and the parameters passed to add() function are -2 and -3.

Simple right? We have tested a unit or part of the entire program. You can do the same with multiply() function. The purpose of this demo was to make you understand what a unit means in unit testing. So, the main objective of here is to verify the internal design and internal logic, internal paths of the software project in small chunks. The unit testing framework that I used in this demo is TestNG. There are various other unit testing frameworks for various programming languages.

Best Unit Testing Frameworks

Some of the popular unit testing frameworks are:

  • JUnit: It is an open-source framework for a test-driven development environment, specifically designed for Java programming language.
  • NUnit: It is one of the most popular unit-testing frameworks for C#.
  • TestNG: Designed for Java programming language, it resembles JUnit and NUnit but offers some new functionalities which make it more powerful and easier to use.
  • HtmlUnit: It is one of the most popular frameworks for JavaScript. It is used for testing web applications that are used within frameworks like JUnit and TestNG.
  • Unitest: Inspired by the JUnit framework, this framework supports test automation and acts independently of the tests from the reporting environment. It is one of the most popular unit-testing frameworks for Python.

Apart from these, there are a lot of other frameworks. With this, we have reached the end of the blog. Hope the things that you have learned here today will help you as you head out on your software testing journey.

If you found this article relevant, check out the live-online Selenium Certification Training by Edureka, a trusted online learning company with a network of more than 250,000 satisfied learners spread across the globe. 

Got a question for us? Please mention it in the comments section of this article and we will get back to you.


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