Functional and Usability Testing: What is the difference?

It never ceases to amaze me as to how many people (including testers) struggle to understand the difference between Functional and Usability testing.

Functional testing is carried out to ensure that the product behaves according to the functional requirements and does not take into consideration design principles. This entails a series of tests which perform a feature by feature validation of behaviour, using a wide range of normal and erroneous input data. In contrast, Usability testing focuses on customer acceptance and how well the customer can use the product to complete the required task. Usability testing investigates all aspects of the usability of a product, including overall structure, navigation flow, layout of elements on a page, clarity of content and overall behaviour.

The relationship between functional and usability testing: usability testing needs to come after functional testing (and fixing of functional problems). Performing usability testing on functionally flawed products only unearths functional problems, which leads to frustration for the participants who are struggling with bugs when trying to complete a task. It hinders the participants, it negatively influences their perception (and hence their feedback etc), and it invalidates the usability aspect of the results.

Both functional and usability testing require very different mind sets from the person testing and ideally should not be carried out by anyone involved in the development of the product. Where functional testing requires the mindset of “CAN I do what I need to do, does this product work?” Usability testing is more about ‘usability’ than it is about ‘testing’ (given that ‘testing’ inevitably seems to bring about visions of functional testing first and foremost) and needs to have the mindset “HOW can I do what I need to do, does this make sense?”

Usability testing participants complete a number of key tasks that users of a product are expected to be able to complete using the product. After each task has been completed, participants are asked to answer a number of questions related to the task. These questions include multiple choice questions about task completion success or failure, ease of completing the task, and rating of any other statements that may be relevant. For instance, rating how complete, useful, and relevant information on a page is. Participants are also encouraged to use the “think aloud/write down” method to share their comments, feedback, and concerns. This information is very helpful in determining the ‘why’ behind certain usability stumbling blocks, and the value you get from this is only increased when the testing comes from carefully selected participants who match your target audience.

I hope this post goes some way to help you identify the differences between Functional and Usability testing, if you have any thoughts on this subject, I welcome your comments. If you would like to discuss how I could help maintain or even improve your current QA function, while reducing the overall cost of quality, please feel free to reach out to me - [email protected].