Which level of tester independence is considered most independent?

The option indicating that tests designed by someone from a different company represents the highest level of tester independence is accurate because it emphasizes the most significant separation from the development process. When tests are created by an external entity, there is a complete detachment from the influence of those involved in the development, which minimizes potential biases and preconceived notions about the software under test.

This level of independence is crucial as it allows for an objective evaluation of the system, ensuring that the testing process is impartial. The external testers approach the software without prior knowledge or assumptions, which can enhance the chances of identifying defects that internal stakeholders may overlook due to familiarity.

While tests designed by another team member or someone from a different department have some level of independence, they still operate within the same organizational context and may retain some insights about the system that could impact their objectivity. Thus, the option highlighting testers from a different company represents the pinnacle of independence in testing scenarios.