What is one of the principles of testing mentioned in the standards?

One of the key principles of testing is that defects cluster together. This principle highlights the observation that in many software applications, a small number of modules or components are often responsible for a large number of defects. This clustering means that if a defect is found in one part of the software, it increases the likelihood that other defects may also be present in the same area or component.

Understanding this principle helps testers focus their efforts more effectively by concentrating on high-risk areas or components that are prone to errors. Such an approach can lead to more efficient testing processes, as resources can be allocated to where they are most likely to uncover additional defects, ultimately improving the quality of the software.

The other options do not align with established testing principles. For example, the incorrect assertion that testing can assure the absence of defects does not recognize that while testing can identify defects, it cannot guarantee their complete absence. The belief that software can always be exhaustively tested overlooks practical constraints like time and budget. Lastly, stating that testing serves no purpose if the software is usable dismisses the necessity of testing for identifying defects that can affect future use, performance, or maintainability, regardless of current usability.