Unit Testing Vs System Testing | Top Key Differences

Have you ever wondered about the different layers of testing that ensure your favorite apps and software run seamlessly? Well, two crucial players in this game are unit testing and system testing. Here, we will focus on unit testing vs system testing. 

Before going into the deep details, let’s start with the fundamentals. Imagine you’re a chef making a delectable dish. Before serving it to your guests, you taste and check if each ingredient is just right. Unit testing is like that meticulous taste test in software development. It focuses on testing individual units of code, ensuring they function perfectly in isolation.

Now, imagine you’re overseeing an entire restaurant operation. System testing takes a step back and evaluates the restaurant as a whole. That is, checking the entire culinary process, from the kitchen to the dining area. In system testing, the focus isn’t on individual units of code but rather on the whole application.

Now, let’s discuss other differences between unit and system testing in detail.

Introduction To Unit Testing Vs System Testing

Unit testing and system testing are two different levels of software testing, each serving a specific purpose in the software development process. Now, let’s see how they differ,

What is Unit Testing?

Unit testing is a type of software testing that verifies the individual units or components of a software application to make sure they work as intended. As the name suggests, a unit refers to the smallest individual part of a software program, which could be a function, method, or component.

Who Performs Unit Testing?

Unit testing is performed by developers. In simple terms, developers will test their code to check if it is working correctly and is doing its purpose. It is the only type of testing where only developers perform testing.

Example of Unit Testing

Let’s take a Java code snippet that performs basic arithmetic operations,

Unit testing vs system testing

Now, to test the code, the developers will enter two random inputs, ‘a’ and ‘b’ (Example: 5 and 6), to test the code. If the outputs are correct, then the code is accurate.

What is System Testing?

System testing is a type of software testing that evaluates the overall functionality of a complete and integrated software application. Here, the entire application will be tested, unlike unit testing. 

System testing is performed to make sure that the software application, as a whole, meets the specified requirements and functions correctly in its intended environment.

Check out the difference between system testing vs integration testing

Who Performs System Testing?

System testing will be performed by Quality Assurance testers (QA). They test the whole application after every component is integrated to make sure the application works as expected without any defects.

Example of System Testing

Let’s consider an example of system testing for a web-based test automation platform – Testsigma.

System testing example

Now, the QA team will test every functionality of the web application, from login, signup, and other internal features to logout.

Testsigma - Test automation platform

Comparison: Unit Testing Vs System Testing

Both system testing and unit testing are vital components of a comprehensive software testing strategy. Let’s take a look at how unit testing is different from system testing in detail here,

Unit TestingSystem Testing
Focuses on testing individual units or components of an application.Evaluates the entire application as a whole after every component is integrated.
Tests are performed in isolation from the rest of the application.Tests the integrated system with all components working together.
It is white-box testingIt is black-box testing
Developers usually write and execute unit tests.Testers or QA professionals typically perform system testing.
Helps validate the correctness of a specific unit/component.Helps validate if the entire application meets specified requirements.
Test cases are developed by developers based on code and design specifications.Test cases are developed by testers based on functional requirements and use cases.
Focuses on code coverage, ensuring that every line or function is tested.Emphasizes functional coverage, ensuring all user requirements are met.
Detects and fixes bugs and issues at an early stage of development.Verifies that the system works as intended from an end-user perspective.
Common unit testing frameworks include JUnit, NUnit, TestNG, PHPUnit, etc.Various tools can be used for system testing, including Testsigma, Selenium, TestComplete, etc.
Here, developers will test only the individual methods or functions in a class.Here, the QA team will test features like user interfaces, APIs, databases, etc.
It can be automatedIt can be automated and easily integrated into the continuous integration and deployment pipeline.
A single-module testing approach is used to perform unit testing.Bottom-up approach and top-down approach testing are used to perform system tests.
It does not support parallel testing as a single unit is tested.It supports parallel testing as system testing tests multiple units in parallel.
It is easy to find defectsIt is difficult to find defects.
It requires less resources for testingIt requires more resources for testing
The cost of unit testing is lessThe cost of system testing is high when compared to unit testing
The visibility of code details is providedThe visibility of code details is not provided

Both types of testing, along with other types of testing, are used to validate software applications thoroughly. 

Check out the difference between system testing vs end-to-end testing in detail – Read more

Key Differences Between Unit Testing and System Testing

Here are the key differences between unit and system testing,

Unit Testing

  • Focuses on testing small parts or modules of the software.
  • The developer runs unit tests and can see the code details.
  • Less resources are required.

System Testing

  • Tests the whole software after every module is integrated.
  • QA tester runs system tests.
  • More resources are required. That is, for efficient system testing, you will need highly skilled testers and sometimes, test automation tools like Testsigma too.

Check how test automation with Testsigma can help you achieve maximum ROI.


Both system testing and unit testing are crucial to software development. Balancing both in your testing strategy guarantees a robust, reliable, and high- application.

Remember, it’s not about system testing vs unit testing but rather about creating a quality product that tops the software market. So, focus on creating a robust testing strategy. Always automate to speed up your testing process. Sign up to Testsigma and start automating your tests.

Frequently Asked Questions

What is unit testing in system testing?

Unit testing focuses on testing individual units of code, while system testing involves testing the entire software system in a comprehensive manner. Unit testing is also called white-box testing, while system testing is also called black-box testing.

What is the one major difference between unit testing and integration testing and system testing?

Unit testing, integration testing, and system testing differ in what they focus on and the scope of the testing process.

  • Unit testing tests the individual units or components of a software application. 
  • Integration testing evaluates the interactions and interfaces between different units or components of the software. 
  • System testing evaluates the entire software application as a whole, including all integrated components, to ensure that it meets the specified requirements.

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