Discerning the Difference: Functional Testing vs. Non-Functional Testing

A few weeks ago, we shared a short five-step guide with you on functional testing. What we didn’t discuss, however, is non-functional testing. So, what’s the difference between the two? After all, they both share the word “functional,” so what’s really going on here? Before you go around telling everyone, “Oh, yeah, I know all about the two. How difficult can it be? They’re both around functional testing,” let's take a moment to break it down and discuss the discrepancies between the two.

Now, before we go into logistics, here is the primary difference between the two we want you to know: Functional testing checks specific functions of the software application, while non-functional testing checks the non-functional aspects of the application. 

Functional Testing 

Goal: Functional testing tests the functionality of the software application against business requirements – without any knowledge of code – and determines if the application meets business specifications such as integrations, user commands, business processes, data manipulation, etc. 

Flow: Functional testing is traditionally executed first – before non-functional testing. 

Types of Functional Tests:

• Regression Testing
• Black Box Testing
• Integration Testing
• Acceptance Testing
• Unit Testing
• Smoke Testing
• Interface Testing

Functional Testing Checklist Examples:

• Are there any broken links or orphaned pages?
• Does the application’s basic functions meet user requirements?
• Can a user enter valid values in both fields during login?
• Do dropdown menus function as per user requirements?
• Are validation errors displayed in the correct position?

Non-Functional Testing

Goal: Non-functional testing tests external aspects of the software application and verifies its quality attributes such as speed, scalability, reliability, performance, etc. 

Flow: Non-functional testing is executed after functional testing has been carried out. 

Types of Non-Functional Tests:

• Load Testing
• Stress Testing
• Performance Testing
• Reliability Testing
• Usability Testing
• Scalability Testing
• Compliance Testing
• Endurance Testing
• Compatibility Testing
• Security Testing

Non-Functional Testing Checklist Examples:

• What is the acceptable threshold for downtime?
• How well does the application work in different browsers and its versions?
• How quickly is the application able to recover in case of system failure?
• How easily can the application be altered, if needed, after deployment?
• Is the application intuitive for users? How much time is needed for them to learn how to use it?

Conclusion

These are just some of the differences between functional testing and non-functional testing. Functional testing essentially tests whether the software application meets user requirements, while non-functional testing tests whether the software application meets user expectations. Both are necessary to ensure a quality product is released to your customers. Without both tests, you run the risk of releasing a product that will ultimately fail – losing you loyal customers and overall profit.