Independent testers are external to the organization, either working on-site (in-house) or off-site (outsourcing). How independence of testing is implemented varies depending on the software development lifecycle model. For example, in Agile development, testers may be part of a development team. In some organizations using Agile methods, these testers may be considered part of a larger independent test team as well. In addition, in such organizations, product owners may perform acceptance testing to validate user stories at the end of each iteration.
Potential benefits of test independence include:
- Independent testers are likely to recognize different kinds of failures compared to developers because of their different backgrounds, technical perspectives, and biases
- An independent tester can verify, challenge, or disprove assumptions made by stakeholders during specification and implementation of the system
- Independent testers of a vendor can report in an upright and objective manner about the system under test without (political) pressure of the company that hired them
Potential drawbacks of test independence include:
- Isolation from the development team may lead to a lack of collaboration, delays in providing feedback to the development team, or an adversarial relationship with the development team
- Developers may lose a sense of responsibility for quality
- Independent testers may be seen as a bottleneck
- Independent testers may lack some important information (e.g., about the test object)