Functional Testing vs Non Functional Testing: Definitions & Differences

When it comes to functional testing vs non functional testing, the comparisons between them cannot be avoided. In this blog, we will have an overview of the key differences between functional testing and non functional testing.

Functional Testing vs Non Functional Testing: What Are They?

Functional testing is a type of software testing that ensures every function of an application works according to the requirement specification. Testers check each functionality of the application by providing appropriate input, verifying the output, and comparing the actual results to the expected results. The testing also covers a wide range of areas such as User Interface, APIs, Database, security, client/server applications, and functionality of the Application Under Test. Both manual and automated testing methods can be used for functional testing.

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Non-functional testing is to check the non-functional aspects of a software application such as performance, usability, reliability, etc. It aims to test the system's readiness according to non-functional parameters, which are not addressed in functional testing. For example, non-functional testing could include testing how many users can simultaneously log in to the software.

Functional Testing vs Non Functional Testing: What are the Key Differences?

Functional and non-functional testing are two different approaches to software testing, each with its own area of focus and testing types. Let’s focus on the differences between them.

  • Testing areas are different

Functional testing focuses on validating the output of an application, product, or feature within the product. It ensures that each step in the product lifecycle aligns with expected outcomes and requirements. Non-functional testing’s aim is to check the internal behavior of an application or product, including its ability to withstand different operating conditions and environments.

  • Testing types are different

Functional testing includes unit testing, regression testing, integration testing, system testing, and acceptance testing. Non-functional testing primarily consists of performance testing, load testing, security testing, stress testing, recovery testing, and volume testing.

  • Customer expectations are different

Functional testing focuses on meeting customer requirements, while non-functional testing aims to validate the customer experience of an application. Non-functional testing considers customer feedback a critical driver of test case planning and covers multiple areas to ensure that the application meets or exceeds customer expectations.

  • Different levels of automation

End-to-end automation testing is possible for both functional and non-functional testing. However, non-functional testing offers easier automation with the latest test automation tools, making it more cost-effective in the long run.

Testing cost is different

Functional testing is easier to manage with manual testing but becomes expensive in the long run. Non-functional testing offers the advantage of easy automation with the latest test automation tools, saving money in the long term.

  • The way to achieve is different

Non-functional testing can be complex from the requirement-gathering perspective, as it requires test engineers to have a thorough understanding of the product's end-to-end usage context. Functional testing offers a straightforward path to defining the exact requirements that test engineers must validate with the application.

Here we offer two examples to help you understand these two types of testing more clearly:

Functional Testing:

Consider a web application that allows users to register for an account, log in, and upload photos. Functional testing of this application would involve testing each of these functions to ensure they work as expected. For instance:

  • Registration: Testers would provide appropriate inputs (e.g., name, email, password) and verify that the registration process completes successfully, the user account is created, and the user can log in using the provided credentials.
  • Login: Testers would provide the email and password used in registration and verify that the user can log in successfully, access their account information, and log out.
  • Photo upload: Testers would verify that users can upload photos, view uploaded photos, and delete photos from their accounts.

Non-Functional Testing:

Consider an e-commerce website that sells products to customers. Non-functional testing of this website would involve testing the website's performance, usability, and security. For instance:

  • Performance testing: Testers would simulate a high volume of users accessing the website simultaneously to verify that the website can handle the expected traffic without crashing or experiencing slowdowns.
  • Usability testing: Testers would evaluate the website's user interface, navigation, and user experience to ensure that it is intuitive and easy to use for customers.
  • Security testing: Testers would assess the website's security measures, such as encryption of user data and protection against cyber attacks, to ensure that customer information is kept safe and secure.
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