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Functional Testing vs Non-Functional Testing

by support@1lyqa.com

Testing is a buzzword in the software industry. According to Frost & Sullivan, the software testing market is expected to grow at 14% CAGR in the next few years with the rise of agile testing and DevOps. The entire software completely depends on this phase of the process. The system needs to be tested on regular intervals to ensure that it executes the process defect free. So, in this article, let’s compare the two major types of software testing based on certain parameters.

Below are the topics that I will be discussing in this Functional testing vs Non-Functional testing article:

  • What is software testing? Why do we need it?
  • Types of software testing
  • Functional vs Non-functional testing on Different Parameters
  • Conclusion

Before comparing Functional testing & Non-functional testing, let us know the process of software testing.

What is Software testing?

Technology in recent days has enhanced so much that most of our day to day activities are done using machines and these machines need to be tested on regular intervals so that the cost of this work is reduced. Software Testing is a process of evaluating the functionality of a software application to find if there are any bugs in the software or not. It checks whether the developed software meets the specified requirements and detects any defect in the software in order to produce a quality product. Testing is, evaluating a system in order to identify any gaps, errors, or missing requirements contrary to the actual requirements.

Why do we need Software testing?

If the software used by any organization works fine without any drawback, it profits the user as well as the organization for providing valuable applications. So, all the applications developed by the organizations should be tested regularly to verify if it is running as per the user requirements.

  • Testing of software is an intellectual task for the testers to perform.
  • Increases the quality of the product developed.
  • Requires lower maintenance cost and therefore results in more accurate, consistent and reliable results.
  • Helps in providing an effective performance for the software application or product.
  • It ensures that the application should not result in failure.

Types of Software testing

Software testing is a pool of knowledge and endorsement and it is a widely used process all around the world. You might wonder what are the different types that exist.

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Testing is an integral part of any successful software project. The types of software testing depend on various factors which even includes the project requirements, budget, timeline, expertise, and suitability. The different Types of software testing play the key role where the tester determines the right testing for appropriate applications.

Software testing is broadly divided into two major types: Functional testing and Non-functional testing which are further divided into various types. Let’s understand each one of them in detail.

Functional Testing

Functional testing is a type of software testing where the system is tested against the functional requirements or specifications like the technical details, data manipulation and processing, and other specific functionalities. You might think, functional testing just refers to testing a function (method) of your module or any class but that’s not what it does. It tests a slice of the functionality of the whole system.

  • It is also a type of black-box testing that holds the test cases according to the specifications provided by the software component under test.
  • Black box testing is a method of software testing which helps in examining the functionality of any application without peering into its internal structures or the implementation process. It means that the user will not know the internal process that takes place while testing a case.
  • This type of testing checks whether the application works as per the user need/requirement or not.
  • Functions (features) are tested by feeding the input and examining the output of the system.
  • Functional testing is more effective when the test conditions are created by the user as per business requirements.
  • This type of testing helps in identifying functions that the software is expected to perform, create the input data based on the system’s functional specifications, determine the output based on the requirements, execute the test cases and compare the actual and expected outputs.

Types of Functional Testing

Let’s take a look at different types of functional testing. They are namely:

  1. Unit testing
  2. Integration testing
  3. System testing
  4. Interface testing
  5. Regression testing
  6. User-acceptance testing

Now, let’s see each one of them in detail

Unit testing: A unit is the smallest testable part of any software. It usually has one or a few inputs and a single output. It is a level of software testing where individual units/components of the software are tested. The main purpose is to validate each unit of the software, performs as designed.

Integration testing: It is a level of software testing where individual units are combined and tested as a group. The main purpose of this type of testing is to expose faults in the interaction between integrated units.

System testing: It is a level of software testing where the complete and integrated software is tested. The purpose of this test is to evaluate the system’s compliance with the specified requirements. It is a series of different tests whose sole purpose is to exercise the system.

Interface testing: It is a level of software testing which verifies whether the communication between two different software is done correctly.

Regression testing: Regression testing verifies that a code change in the software does not have an impact on the existing functionality of the product.

User-acceptance testing: It is a level of software testing where a system is tested for acceptability. The sole purpose of this test is to evaluate the system’s compliance with its business requirements and assess whether it is acceptable for delivery. It checks whether the software can handle the required tasks in real-world scenarios.

Now, let’s see what is Non-functional testing and see what exactly it does to test software.

Non-functional Testing

Non-functional testing is another type of software testing which is used to check the non-functional aspects like performance, usability, reliability, etc. of a software application which is not tested using functional testing.

  • Non-functional testing helps in testing the readiness of a system.
  • It defines the way a system operates, rather than specific behaviors of that system. This is totally in contrast to functional testing, which tests against functional requirements that describe the functions of a system.
  • Basically, non-functional testing is done to check and evaluate all the non-functional parameters which are not covered under functional testing.
  • Non-functional Testing is equally important as Functional testing.
  • All the non-functional parameters such as speed, scalability, security, reliability, and efficiency of an application are tested under the non-functional testing.
  • It makes an application robust and prepares it against certain vulnerabilities.

Types of Non-Functional Testing

Let us see what are the different types of Non-functional testing. They are namely:

  1. Documentation testing
  2. Installation testing
  3. Performance testing
  4. Reliability testing
  5. Security testing

Let’s learn about each one of them in detail

Documentation testing: It helps to estimate the required testing efforts and track the requirements. Software documentation includes a test plan, test cases, and requirements section. It tests the documented artifacts.

Installation testing: It is a type of quality assurance work in the software industry that converges on what customers will need to do to install and set up the new software successfully. It checks if the software application is successfully installed and is working as expected. The testing process may involve full, partial or upgrades install/uninstall processes.

Performance testing: It is defined as a type of software testing that is used to ensure that the software applications will perform well under their expected workload. Performance testing is considered as a heart of Non-functional testing. It is further divided into a few types.

Types of Performance testing:

  • Load Testing is a type of performance testing conducted to evaluate the behavior of a system at an increasing workload.
  • Stress Testing is a type of performance testing conducted to evaluate the behavior of a system at or beyond the limits of its anticipated workload.
  • Endurance Testing is a type of performance testing conducted to evaluate the behavior of a system when a significant workload is given continuously.
  • Spike Testing is a type of performance testing conducted to evaluate the behavior of a system when the load is suddenly and substantially increased.

So, this is about performance testing. Now, let’s take a look at the other types of non-functional testing.

Reliability testing: It assures that the product is fault free and is reliable for its intended purpose. It is about exercising an application so that the failures are discovered before the system is deployed.

Security testing: It is a variant of software testing which ensures that the system and applications of the organization are free from loopholes. Security testing is about finding all possible weaknesses of the system which might result in a loss of information.

This is all about the different types of Non-functional testing. Now let us move forward and compare functional & non-functional testing on various parameters.

Parameters to compare Functional and Non-functional testing

To point out the differences between the major types of software testing, we will compare them based on a few parameters like their

  1. Objective
  2. Area of focus
  3. Ease of use
  4. Functionality
  5. Execution

Let’s take a clear look at these parameters and understand how these types of software testing differ based on them

Objective: Functional testing is mainly carried out to verify and validate the software actions such as the login function whereas Non-functional testing helps in verifying and validating the performance of the software.

Area of focus: Functional testing concentrates on the user requirements like what the system should do under a given situation, and it defines the process that takes place whereas Non-functional testing concentrates on the user expectations like how the system is built, how does it interact with the user and so on.

Ease of use: Functional testing is easy to execute, the black box testing where the internal implementation is not known to the user whereas Non-functional testing is easy to execute white box testing where the internal structure/implementation process is known to the user and there is transparency in the operations taking place.

Functionality: Functional testing helps in describing what the system should do whereas Non-functional testing helps in describing how the system should work. It means functional testing provides answers to all what functions in the system whereas Non-functional testing provides answers to all how questions in the system.

Execution: Functional testing takes place before the execution of Non-functional testing. This is because of Functional testing defines all the process and this is executed first whereas Non-functional testing execution takes place only after the execution of Functional testing because only if the system is defined, you can proceed further and customize it accordingly.

So, these are the parameters on which Functional testing and Non-functional testing differ from each other.


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Functional testing and Non-Functional testing are the two most important types that play a major role in testing a software. By including functional testing into the equation of testing an application, one can test what the process is up to and what does the system do under any given circumstances. If Non-Functional testing is prioritized, it deals with the performance of the system and describes how the system performs under any given circumstances. Both have their own pros and are limited to some constraints. It is completed dependant on the user as how he wants to test the system.

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