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System Testing and Functional Testing: What’s The Difference?

Testing is consistently regarded as one of the most important aspects of the software development cycle. Before being put into production, the code and the functionality of the product should be tested. This is true whether the testing is performed on just one feature or on the entire product. I believe that every developer would agree with this statement. As a software developer, one of the questions that I frequently find myself pondering is: at what point in the development process should I begin testing my code? I am curious about whether or not it is productive and cost effective to conduct testing on a feature-by-feature basis.


What exactly is meant by the terms “System Testing” and “Functional Testing,” and how do these two terms differ from one another? To put it simply, I consider System Testing to be the process of testing an entire product or an entire section of a product from beginning to end in order to validate the correct operation of all of the features contained in either the product or the section being tested. As an illustration, I might create a spreadsheet that contains the entirety of the specified functionality of a product itemised on a row-by-row basis. I would then test that functionality in each row to determine whether or not the input causes the feature to pass or fail. Therefore, testing a system’s functionality from beginning to end can be interpreted as testing the functionality of an entire system.

On the other hand, I define “functional testing” as “small automated tests that can determine the integrity of a single feature within a section.” Functional testing is a subset of “integrity testing.” For instance, if I know that the scope of a section is set in stone, I will develop a feature and then frequently develop an automated test to verify that the input of a feature produces the output that I am looking for.

This is just one example. Functional Testing classes can be created relatively easily and do not require a significant amount of coding. Automated code testing classes are frequently integrated into the majority of today’s most popular frameworks. The majority of the time, performing functional testing only requires the creation of a testing class, its subsequent execution via the command line or via a testing graphical user interface (GUI), and the subsequent viewing of the test result.

The differences

Testing the functionality of a single component of a product is an example of functional testing, while testing the functionality of the entire product is an example of system testing. Functional testing is distinguished from system testing by the fact that functional testing focuses on a single component of a product.

 Functional TestingSystem Testing
Testing Scopeindividual feature functional testing.testing of the entire system, both functionally and non-functionally.
System IntegrationsMocking may be done to some integrations.Integrations are not mocked.
Test DataUnrealistic test data.Realistic test data.
Test EnvironmentEnvironments for Development.End to end Integrated Environment .
Test EffortLittle testing was done.Additional testing effort
Stakeholderssmall audience and few teams participating.Wider audience with all project stakeholders.

Types of System Testing

Performance Testing

One type of software testing is called performance testing, and its purpose is to evaluate a system’s compliance as well as its speed, reliability, and stability. Testing the system’s performance results in the generation of a report that contains both quantitative and qualitative measurements connected to that performance. This testing approach uses quantitative inputs based on predetermined key performance indicators (KPIs) in an environment with a restricted range of possibilities.

Load Testing

One type of software testing is known as load testing, and its purpose is to determine how a system operates when subjected to a significant amount of pressure. This testing method uses quantitative inputs within an environment with a restricted range of possibilities. The maximum load that can be supported by the product before it starts to degrade will be determined by load tests.

Stress Testing

A testing that is performed to check the robustness of the system at or beyond the system’s limits (either the lower limit or the higher limit) of its specified requirements. This method of testing requires the application of variable and undetermined loads as input.

Scalability Testing

Scalability Testing is a subcategory of software testing that is carried out to evaluate a system’s or product’s functionality in terms of how well it can adjust to an increase in the number of user requests being processed at once.

Automated Tools for System Testing

System testing, as the name suggests, examines many facets of a system, including the system’s usability, performance, and security, amongst other things. In order to make the most efficient use of both time and resources, the testing of each component of a product makes extensive use of various automated testing tools. Among the most common tools are:

  • Rational Integration Tester
  • Steam
  • WebLOAD
  • LoadRunner
  • Netsparker
  • BeEF

Let’s now perform functional testing to determine how it functions. Functional testing primarily consists of graphical user interface verification using predefined test data and various business scenarios as test cases.

Types of Functional Testing

Unit testing. 

Check that each component of the software programme can function correctly on its own before moving on to testing the entire software package. The function of a unit is validated by performing unit testing, which ensures that the inputs (one to a few) result in the single output that is desired. This type of testing lays the groundwork for more complicated integrated software. Unit testing, when carried out correctly, can lead to higher quality application code and can speed up the development process. Test automation is frequently utilised by developers in the course of unit test execution.

Smoke testing. 

Smoke testing is a subtype of acceptance testing that serves as an initial check to ensure that a newly built version of software and all of its essential features are stable. If the smoke tests are successful, then the build can move on to the next phase of testing. The purpose of smoke testing, which is also known as build verification testing, is typically to determine whether or not new or crucial functionality satisfies its objective. In the event that the tests are not passed, it is safe to assume that “where there’s smoke, there’s fire,” and additional development work will be necessary.

Sanity testing. 

A type of regression testing that quality assurance professionals perform on new versions of stable builds in order to validate either newly added functionality or bug fixes. Sanity testing differs from smoke testing in that it does not follow a script and focuses specifically on the part of the programme that has been modified by new code. Both smoke testing and sanity testing serve the same purpose of ensuring that a build is ready for further testing.

Regression testing. 

Even if functional tests are successful at least once, this does not guarantee that they will always be successful. You should run regression tests whenever developers commit new code or change a feature to ensure that the software continues to function as intended after the change. When changes are made to a product, regression testing can help ensure that the product remains stable. Automated regression testing is common practise.

Integration testing. 

Testing at the unit level is frequently done in conjunction with testing at the integration level. Integration testing is a type of quality assurance testing in which QA professionals verify that the individual modules of code work properly together as a group. A large number of today’s applications are powered by microservices, which are self-contained programmes that are created to perform a particular function. These microservices have to be able to communicate with one another; if they can’t, the application won’t work the way it was supposed to. Integration testing is how testers ensure that all of these components can operate and communicate with each other without any issues.

White-box testing. 

White-box testing is a type of software testing that occurs when the developer or tester has access to the internal infrastructure, code, and design of the software being tested. This strategy employs several distinct kinds of functional testing, including unit, integration, and system testing, among others. When an organisation employs a testing strategy known as white-box testing, multiple facets of the software are put through their paces, including predefined inputs and expected outputs, as well as decision branches, loops, and statements in the code.

Black-box testing. 

Testing against a system in which the internal code, paths, and infrastructure are not visible is known as black-box testing. This type of testing stands in contrast to white-box testing. Therefore, testers make use of this method in order to validate anticipated outputs against specified inputs. Black box testing can be applied to any scenario in which a quality assurance professional does not examine the source code prior to testing. With the help of black-box testing, an organisation is able to test software in the same manner in which a customer would interact with it. Depending on the purpose of the test, black-box testing can involve a wide range of testing approaches, including both non-functional and functional testing.

Example of Functional Testing and System Testing

Functional Testing example

We will provide examples for functional testing, including unit testing, integration testing, and regression testing. A restaurant needs an app that allows customers to place orders at their tables without the assistance of a server so that they can perform unit testing. The “add to order” function would be examined by the software developer using a unit test. Other individual functions, such “remove from order” and “submit order,” among others, would also be covered by unit testing.

Banking apps that go through integration testing often have a feature that lets users start a savings account. It enables users to transfer funds between their main account and their savings account at their discretion. The testers must perform integration testing to make sure that the transactions between the two distinct modules go easily and appropriately. Since these are separate modules, this is necessary. The next step was for a food delivery app to add a function to help users add multiple promotions on top of each other. This was done as part of the app’s regression testing. It is necessary to conduct a regression test in order to guarantee that the checkout and payment procedure will not be disrupted.

System Testing Example

A manufacturer of automobiles does not produce the vehicle in its entirety. Each individual component of the automobile, such as the seats, steering, mirrors, breaks, cables, engine, car frame, wheels, etc., is manufactured independently. After each product has been manufactured, it undergoes a process known as “unit testing” to determine whether or not it functions in the manner that was intended for it to function. Now, when each part is assembled with another part, the assembled combination is checked to see if the assembly process has produced any side effects to the functionality of each component and whether or not both components are working together as expected. This type of testing is referred to as integration testing. Even after all of the components have been assembled and the vehicle appears to be ready to drive, it is not.

The entirety of the vehicle needs to be examined to ensure that it satisfies the requirements that have been established. These requirements include ensuring that the vehicle can be driven without any hiccups, that its brakes, gears, and other functionality are operating correctly, that it does not exhibit any signs of wear and tear after being driven nonstop for 2500 miles, that the colour of the vehicle is popular and well-liked, that it can be driven on any kind of road, including smooth, rough, sloppy The client was convinced about the efforts that would be required for the system test after the example worked as expected. I related the story as an illustration to stress the significance of performing these tests.

When We Need To Use System Testing or Functional Testing?

Therefore, under what circumstances should one employ System Testing as opposed to Functional Testing? In each and every iteration of the software development cycle, I believe that you ought to incorporate some kind of system testing. On the other hand, functional testing is something that must be done based on the discretion of the development team and how a project is progressing. It’s possible that some teams have more time and money available to devote to functional testing than others. Every development cycle is unique, and despite the fact that in an ideal world we would all like to perform Functional Testing, there are times when it is impossible to do so due to limitations imposed by both time and money.

I have found that I can rely on a set of three rules of thumb in order to determine whether or not I should perform testing while I am in the process of developing a new product. This is something that I discovered while I was working on finding the right testing methodology for my needs.

First and foremost, I should only carry out functional testing on a single feature if I am confident that the functionality of that feature has been thoroughly outlined and will not be altered in the near future. Number two, if I observe that there is uncertainty regarding the manner in which the features contained within a specific section ought to be defined, then I postpone carrying out functional testing and instead carry out system testing on that specific section once it has been finished. Before sending a product into production, you should always, number three, put it through some kind of System Testing first, no matter what.


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System Testing And Functional Testing. (2016, March 6). Agnostic Development. Retrieved February 13, 2023, from https://www.agnosticdev.com/blog-entry/testing/system-testing-and-functional-testing

What is functional testing? Types and real-life examples. (n.d.). What Is Functional Testing? Types and Real-life Examples. Retrieved February 13, 2023, from https://katalon.com/resources-center/blog/functional-testing


45 Functional Testing Types with Examples. (2021, May 25). Applause. Retrieved February 13, 2023, from https://www.applause.com/blog/functional-testing-types-examples

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