When assembling a test team to work on an enhancement to an existing system, which of the following has the highest level of test independence?

The highest level of test independence is found in someone who has no prior affiliation or bias towards the system being tested. In this case, the contract tester who has never worked for the organization before fits this description perfectly. Since this individual is new to the organization, they come with a fresh perspective and can assess the system without preconceived notions or influences from past experiences within the company. This independence is crucial as it allows for an objective evaluation of the system's enhancements.

Other members of the team, such as the business analyst or the permanent programmer, may possess inherent biases based on their previous involvement with the original system or the new code. Similarly, the permanent tester, despite being a seasoned expert, might carry biases from their experiences with the original system and their familiarity with its defects. These factors can inhibit their ability to challenge assumptions or critically assess changes without being influenced by their history with the system. In contrast, the contract tester's fresh perspective allows for an unbiased approach to testing, making them the most independent choice.