Majority of the testers will focus more on testing the product against client requirements – which we mention as Functional Testing and pay less attention to non-functional testing. Non-functional requirements often play a significant role in differentiating between a product that is well received by customers vs one that may not do well in the market place. Some of the key non-functional requirements include Usability, Performance, Security, and Interoperability & Compatibility. To be more precise, Functional requirements define what a system will do while Non-functional requirements describe how the system will do it. Non-functional requirements characterize the behavior that is required in functional requirements

There are some situations which really makes the QA users and project managers to think about importance of non-functional testing for their products. A few of them would be