Which level of tester independence is considered most independent?

The level of tester independence considered most independent is when tests are designed by someone from a different company. This scenario provides the greatest separation from the development team and the context in which the application was created.

When testers are from an external organization, they are not influenced by the internal processes, politics, or development practices of the team that created the application. This external perspective allows them to approach testing without preconceived notions about the system, leading to diverse approaches and potentially identifying issues that internal testers might overlook. Their independence can lead to more objective and thorough evaluations of the product's functionality and performance.

In contrast, tests designed by the author, another team member, or even someone from a different department, while more independent than the author, still carry varying degrees of familiarity with the product and its development context. Each of these options can lead to bias or influence, which can limit the effectiveness of the testing process.