What is Unit Testing?

A unit test is a test that exercises a single unit of functionality in an application. It’s the software equivalent of a physical test, where you run all the same steps that you would run in your code to verify that something is working correctly. There are several benefits to writing unit tests.

Unit testing is a software development practice that improves the quality of your code by ensuring it is free from errors. This article gives you an overview of unit testing, explains how to use TDD, and introduces some best practices for effective unit testing.

What is unit testing?

In software, testing process unit testing means testing the smallest individual unit or component to validate whether the smallest unit is performed as designed. the unit test is performed during the development or coding stage to verify its correctness, and the developers mainly perform it.

In different development methodologies like (SDLC, STLC, and V Model) unit testing is the first testing phase before doing any other testing process. Unit testing is one type of white box testing technique.

The developers do unit testing during the coding to verify whether the piece of written code behaves according to the design. Sometimes, doing unit testing helps reduce the fixing cost during system testing integration testing. So, doing proper unit testing saves an organization both time and investment.

How Does Unit Testing Work?

It is generally necessary to use a mock to test functions. Without mocks, it would be impossible to test the function properly. Testing is dependent on mock objects. Mock objects can be used to fill in for missing parts of a program, such as when functions require variables and/or objects that are not yet created. The purpose of a mocking library is to fill in missing functionality for an object or program unit by using objects that behave like those on which the function under test depends.

Unit Testing Techniques

The Unit Testing Techniques are mainly categorized into three parts.

White Box Testing

It is a test that focuses on the application’s internal structure and verifies particular conditions or exceptions. For example, it can test boundary value cases, error conditions, and object invariants. It is also known as the Glass Box Test.

Black Box Testing

It is a test that focuses on the application’s functionality and verifies functionality under certain pre-defined conditions. For example, it can be used to test pre-defined user scenarios. It is also known as the Black Box Test.

Grey Box Testing

It is a combination of black-box and white-box testing. It focuses on the boundary value cases, i.e., verifies functionality and internal structure.

There are different Code coverage techniques used in Unit Testing. we have noted down various Code coverage techniques:

Statement Coverage: This technique tests the lines of code executed when a program is run and the branches (decisions) taken by those lines of code.

Branch Coverage: This technique tests the condition under which each branch in a program is executed. Each branch is a decision in the code, such as an if-else statement or switch statement, and sometimes also includes loops.

Decision Coverage: This technique tests the different decisions made in a program, along with their associated conditions.

Condition Coverage: This technique tests each condition that causes a particular branch in a program and its associated branches.

Finite State Machine Coverage: This technique is used to test each of the states in a program’s internal finite state machine.

Unit Testing Advantage

Unit testing is carried out very early, so the issue can be found early. So that defects can be fixed early before impacting any other piece of code.

For making unit testing, possible codes need to be modular. This means that codes are easier to reuse, and it also helps to reuse the same code in other required places, so because of this nature, the development also goes faster.

Unit testing helps reduce the cost of bug fixes compared to finding a bug in system testing or integration testing. You are also debugging easily because when a test fails, you only need to debug the latest changes.

Unit testing improves the quality of the code because it identifies the defect before the code goes for integration testing.

Test automation is one of the best practices to increase your application’s stability, reduce costs, and ensure good overall performance. Automated testing minimizes errors so that defective products do not reach customers. Automated testing helps prevent expensive recalls and costly fixes by eliminating these defects early in the process. It also ensures consistent reliability for all users by allowing independent defects to be found as soon as they occur.

Advantages of Unit Testing:

  • Provides detailed information about how individual units function when combined with other units;
  • Identifies errors or faults before the final product is released;
  • Provides a stable, maintainable design;
  • Affords better documentation of code behavior.

Other Benefits include Developing code with good test cases, making it easier to refactor or restructure the system in order to improve the overall quality without affecting existing functionality. It also helps avoid regression bugs introduced during upgrading and debugging production systems.

Unit Test Disadvantage

Unit testing can’t be expected to catch every program error because testing all possible program paths is impossible. We try to find errors from a specific code unit in unit testing. So here, we can’t find integration errors or system-level errors.

  • Test procedures are generally “informal”, so there is no standard way to write them;
  • They tend to be written by developers who understand the application internals but not necessarily how they will interact with each other in different situations. 3-There are often only enough tests to guarantee the correct behavior of units in isolation, not the proper integration of all units into a complete application.

The main problem with unit testing is that it doesn’t guarantee 100% correctness, and it can only be used to test code written so far. New tests must be added after each modification to catch any errors introduced by later modifications. This means that more time and money are required to develop software using this approach – especially when compared to traditional top-down development methods like Waterfall or pseudo-Agile approaches like Scrum (which completely ignore Automated Testing).

Facts About the Unit Test

  • Unit test cases should be independent and not impact any requirement change or enhancement.
  • The naming convention for each unit test case should be clear and easy to understand.
  • There should be a unit test case for each module, and before implementing the change into the module, the module should pass the test.
  • Bugs found during the unit test cases should be fixed before the next phase.
  • Try to cover all paths through the unit test cases and give more attention to the loop conditions.
  • Always use a version control system to track your script’s changes easily.
  • Perform the unit tests more frequently and continuously.

How to Write Unit Tests?

You SHould always write the unit tests with the code so that the developer working on the application can understand what is written there. There is a standard rule for writing unit tests. The testing is derived from a test case that is not dependent on other tests.

When you write the test method for every test that should start with a test, for each operation like reading, clicking, downloading, delete there should be separate methods for each.

Below, you can get such a list of methods:

  • Setup: this method is used to prepare the tests, so before every test, this method is called.
  • tearDown: this method is called at the last of the test execution after all test methods have been called and the result is stored. this method can also be called when an exception occurs.
  • setUpClass: this method is called before an individual class is called.
  • tearDownClass: this method is called when individual methods of a class are completed
  • setUpModule: this method is called before the classes of an individual module run.
  • tearDownModule: this method is called after the classes of an individual module run.

By following such things, we can able to write good unit tests.

Unit Testing Tools

Unit testing is usually done by a programmer using a unit testing tool. These tools provide the framework for running individual tests and collating their results. Some unit testing frameworks provide test cases within the source code, allowing for greater integration into an IDE. There are open-source and commercial tools available:

Here are some unit testing tools broadly used to perform the unit testing.


It is a set of classes that allow developers to create repeatable tests. It was originally created for Java but can be used with other languages.

It is a unit testing framework for Python that uses the XUnit design pattern and is inspired by JUnit. It can be used with Python or any other language that allows the definition of classes and methods.


NUnit is a lightweight, free, open-source unit test framework for all .NET programming languages. It was originally created by Novell in 2002 and was donated to the community in 2005.


Jmockit is a Java mocking framework for unit testing and behavior-driven development. It can be embedded in any JVM language with a JSR-223 (Java API for XML-based RPC) implementation.

It is an open-source unit testing framework by Google inspired by JUnit, with features for testing Google-specific libraries and code. It uses annotations to specify test cases in the source code.


It is a unit-testing framework for Python. It’s implemented on top of the standard unit test module and provides additional utilities that make testing easier. It is a Python port of the popular JUnit framework by Sun Microsystems.

TestNG: It is an open-source framework for writing and executing automated tests of Java code. It was previously known as Novlet and TestNg, and its current name has been valid since 2005.

TestNG was designed to be a simple framework that could provide both easy extensibility and a powerful set of features, such as the synchronization of tests or the option to run only relevant tests, for example. It is developed by the Apache Software Foundation and used in Java projects such as Hibernate, Apache Ant, and Apache Camel.


As you can see, there is a lot of involvement in unit testing. It can be simple or complex, depending on which application type you will test and what testing strategy you will follow. But you can’t ignore the importance of unit testing in the software development process.

Unit testing is widely used in the software development industry. The fact that every developer can use it to test cases or capture exceptions and debug information is a significant advantage. It helps find bugs early and prevents the need for large-scale testing of the already-developed software.

Testing is extremely important in ensuring the software works as designed, but it is not a replacement for good development practices. Many unit testing frameworks will produce false failures unless additional steps are taken to design for testability.

Developers should learn testing principles and get used to the process of writing tests to ensure that they exercise the application code properly. When writing tests, developers should ensure that they are not testing the framework or platform itself but are testing the functionality of their application.

Unit testing is an iterative process and requires the involvement of all development team members, from testers and designers to developers. It improves software design and increases confidence in a product by identifying bugs early on.

Unit testing is no replacement for good design, integration, or end-to-end testing but rather a complement.

After every iteration of the software development lifecycle, unit testing is an important practice that ensures high-quality software.

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