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Software Unit Testing

Testing is done at multiple stages to ensure software quality. The testing of individual software components to verify if they are working as expected is known as unit testing. Thus unit testing is all about validating the specific units of the software.

What is Unit Testing?

Unit testing of the software is conducted by the developers. It is done at early stages of the software development process when each of the software units are not yet integrated. This is the first stage of functional testing of the software. The unit test cases may be executed manually or through automation.

The correctness of each isolated unit developed - function, method etc are verified. The unit testing is done to identify defects at the early stages of software development life cycle (SDLC) to improve the software quality and have a quicker fix for the defects. Each unit of software is tested independently by the developers.

What are the Prerequisites for Unit Testing?

In unit testing, individual software units consisting of methods, functions, procedures etc are tested to check if they are working as expected. An individual unit is validated independently by the developer himself while he is actually working on it. A separate software component can be a specific method, function, procedure, block of code etc.

Once the unit testing has been completed, it moves to the integration testing phase. Bypassing unit testing, leads to higher number of defects detected at the integration, system, acceptance, and beta testing. Thus, unit testing is helpful in understanding software code, and fixing loopholes. The unit test cases consist of the below steps −

  • Design Test Cases
  • Review Test Cases
  • Baseline Test Cases
  • Run Test Cases

Why is Unit Testing Performed?

Th unit testing is performed because of the reasons listed below −

  • It is performed to segregate a piece of code.
  • It is performed to validate the accuracy of the developed code.
  • Unit testing is done to test every function, method, procedure etc in the code.
  • It detects bugs in the early phases of SDLC.
  • It helps the developers to comprehend their code better and find loopholes there.
  • Unit testing enables better reusability of the code.

Types of Unit Testing

The unit testing types are listed below −

Black Box Testing

In black box testing technique, testers are unaware of the internal logic of software, and are only concerned with data input to software and its output.

White Box Testing

In white box testing technique, testers verify all the software functionalities along with the internal code.

Gray Box Testing

The gray box testing is a combination of both black and white box testing.

Different Unit Testing Tools

The different unit testing tools are listed below −

  • JUnit − JUnit is a unit testing framework for Java programming language. JUnit has been important in the development of test-driven development, and is one of a family of unit testing frameworks collectively known as xUnit, that originated with JUnit.

  • NUnit − It is a unit testing framework for .NET.
  • PHPUnit − It is a unit testing framework for PHP.
  • EMMA - It is a free and open source framework working with Java.

Advantages of Unit Testing

The advantages of unit testing are listed below −

  • Unit testing helps the developers to improve the code and make each software component work properly.
  • It allows testing of independent clusters of the software without depending on other clusters.
  • It allows early detection of defects in the initial stages of SDLC, and to fix them quickly.
  • It helps the developers to build confidence on the code they developed by enhancing its quality.
  • Unit testing helps to resolve the defects faster without requiring to wait for the development of all the modules of the software.
  • It assists the developers to refactor the code safely without breaking the existing functionalities.
  • Unit testing saves a lot of time and resources as fixing defects at the early stages of SDLC is easier and faster than at the later stages.

Disadvantages of Unit Testing

The disadvantages of unit testing are listed below −

  • It requires time to develop and maintain test cases for unit testing and modify them as the requirements change.
  • It only identifies defects on individual units of the software and not on the integration of the units.
  • It cannot detect errors in the user interface of the software.
  • Unit testing does not include non-functional requirements of the software such as scalability, security, reliability, responsiveness, usability etc.
  • The quality of the unit testing depends solely on how well the unit test cases are written by the developers.
  • The developers face problems performing unit testing on complex applications as it is difficult to segregate their individual components and verify them.
  • Unit testing does not involve testing of all the execution paths within the tested module.


This concludes our comprehensive take on the tutorial on Software Unit Testing. We’ve started with describing what is unit testing, what are the prerequisites of unit testing, why unit testing is done, types, tools, advantages and disadvantages of unit testing.

This equips you with in-depth knowledge of Software Unit Testing. It is wise to keep practicing what you’ve learned and exploring others relevant to Software Testing to deepen your understanding and expand your horizons.