Final answer:
Stuart Smally with 4 years of experience performing detail testing on an audit team is most likely a senior associate. This position generally requires a few years of experience and involves doing core audit work like detail testing.
Step-by-step explanation:
Given the information that Stuart Smally is a part of the Toyco audit team with 4 years of experience and performs detail testing, it is most likely that Stuart is neither a partner nor a manager, as these positions usually require more experience and involve higher levels of responsibility, such as overseeing the audit process or managing client relationships. Therefore, Stuart is more likely either a staff associate or a senior associate. Considering the amount of experience mentioned, Stuart is most likely a senior associate, as this role typically encompasses individuals who have a few years of experience and are responsible for executing the core audit work, including detailed testing, under the supervision of more senior members of the firm.