Functional vs Non-Functional Testing: why, how and when each improves software development

When things don’t work as intended, they’re less effective. It seems obvious, but it’s a critical point to pay attention to during software development. 

Insisting on well-designed functional and non-functional testing ensures your application is functionally sound and will perform well when used in real life. 

At Groove Technology, we value testing as part of our software development processes because it’s the best way to ensure that both your requirements and your expectations are met.

That limits the chances of technical issues, improves the user experience, and means your systems will actually deliver the outcomes users want and need.

Why is functional and non-functional testing important?

Testing reduces the risk of technical flaws, which reduces the need for technical fixes or customer service support. But it goes far beyond that. 

The practical usefulness and usability of the software applications you want your customers and employees to interact with on a daily basis are vital.

Especially when you consider:

• Up to 77 percent of online shopping carts are abandoned on eCommerce websites, often due to friction in the process.
• More than 10 percent of users uninstall apps primarily due to crashes, bugs and confusion.
• More than a third of employees globally feel their job is harder than it should be due to poor technology and user experience.

If your software doesn’t deliver the result people are looking for in a timely, accurate, and easy-to-use way, what’s their incentive to keep using it? 

Your business suffers through lost sales and reduced productivity when the applications that underpin your success don’t work properly.

Functional vs non-functional testing: how do they differ?

Functional and non-functional testing are both important and complement each other. The fundamental difference is that functional testing assesses what the product does, while non-functional testing looks into how the product works. 

Functional testing is typically conducted first to validate that the software is fit-for-purpose. For example, when you enter the correct login details, you’re taken to the correct welcome dashboard or screen. 

Other examples could include:

• Whether your payment gateway flags an error if you enter an incorrect credit card number?
• Whether the correct amount is applied when you select a shipping type or destination?
• Whether a purchase order sent for approval in the system is received by the right person?

Non-functional testing relates to how the software operates and what it’s like to use—it evaluates qualities including speed, scalability, security, reliability, and efficiency. An example would be how long the welcome screen takes to load, or how many users can log in simultaneously.

How is functional and non-functional testing carried out?

During the planning of an application, you’ll no doubt determine a long list of requirements—functional specifications the software must address to ensure your business objectives can be achieved. 

Testing needs to hark back to these requirements—they’re the reason you’re building, customising or integrating a piece of software in the first place. Determining where testing is needed most may require a prioritisation process. 

There are many types of testing that might be applied to thoroughly validate functional and non-functional requirements. Typically, tests to gauge the success of key functions and performance criteria will focus on using real business inputs, to help simulate your real employee or customer experience.

Testing processes may be manual or automated through the use of various testing tools. 

It may include black box testing—where valid and invalid information is entered to check the validity of outputs—as well as examining the code, checking APIs, the database, the user interface, and how the system performs under stress or recovers from crashes.

Who should do the testing? 

Rigorous functional and non-functional testing is first and foremost a job for qualified software testers with development process expertise. 

Knowing when, why and how to perform certain tests effectively is a reason to ensure your software development work is capably managed and your team includes people with testing experience and skill. 

A specialised team can help you scope a tailored program of testing for your software development project, based on a clear understanding of the business goals, user expectations, budget, and timeframes.

Finding the best tech talent is easier when you’re not constrained by geography or lengthy recruitment and onboarding processes—taking advantage of an outsourced remote team is one approach that saves time and money.

Functional and non-functional testing are not ‘set and forget’

Depending on your software development needs, your application may be in a continuous loop of development, testing, and delivery—in which case, testing expertise, techniques, and tools will be constant requirements over time. 

Other scenarios where functional and non-functional testing will be relevant include when you add new functionality, integrations or add-ons to an application. When software behaviour and performance have the potential to change or break—testing is critical to keep users satisfied.