Software systems are an integral part of life, from business applications (e.g., banking) to consumer products (e.g., cars).

You’ve probably had an experience with software that didn’t go as expected. Besides client dissatisfaction, software that doesn’t work correctly can lead to many other problems: from losing money, time, or business reputation, to injury or death, in extreme cases.

Testing systems and documentation rigorously can help reduce the risk of problems during operation. It also contributes to the software system’s quality if the defects are fixed before the system is released.

Software testing may also be required to meet contractual or legal requirements or industry-specific standards.

Testing allows you to measure the quality of software in terms of defects found (for both functional and non-functional software), requirements and characteristics (e.g., reliability, usability, efficiency, maintainability, and portability).

Testing will give you extra confidence in the quality of the software if it finds few or no defects.

Plus, a properly designed test reduces the overall level of risk in a system.

On the other hand, when testing does find defects, the quality of the software system increases when they’re fixed.

We can all learn from previous projects by understanding the root causes of defects – that’s how processes are improved, which should prevent them from reoccurring and enhance the quality of future systems. Who wouldn’t want that?

A human being can make an error (mistake), which produces a defect (fault, bug) in the program code. If that defect is executed, the system may fail to do what it should do (or do something it shouldn’t), causing a failure.

Defects may result in failures, but that’s not the case for all of them.

Defects occur because human beings are fallible. There is time pressure, complex code, the complexity of infrastructure, changing technologies, and many system interactions. So, of course mistakes will happen.

Failures can be caused by environmental conditions as well – radiation, magnetism, electronic fields, and pollution can cause faults in firmware or influence software execution by changing the hardware conditions.