I hate to bring the Chief Counsel into this one, but:
In your example, the pilot taking a practical test does not meet any of the circumstances for logging PIC time in section 61.51(e). The pilot is neither the sole occupant of the aircraft nor acting as PIC of an aircraft on which more than one pilot is required. That pilot is the sole manipulator of the controls but is not rated and does have privileges for the aircraft. Under the section 1.1 definition, a pilot must be rated in the aircraft to act as PIC. An exception to this rating requirement has existed since the FAA issued section 61.47 (then as 14 C.F.R. § 61.26) on July 3, 1965. 30 FR 8515. In that final rule, the FAA explained that an unrated pilot is qualified to act as PIC during a practical test because that pilot possesses the appropriate experience prior to the practical test for the particular certificate or rating. Though there have been multiple changes to Part 61 in the intervening years, this exception never has been withdrawn.
No similar exception has been made with respect to logging PIC time under section 61.51(e).
It is inconsistent that a pilot is permitted to act as PIC but not log PIC time when both sections 1.1 and 61.51 require that the pilot be rated for the aircraft, and the pilot must possess the appropriate experience prior to the practical test. Therefore, a pilot may log PIC time for the practical test. With respect to the student flight referenced in your letter, the student pilot may log PIC flight time for the practical test for the same reason even though the student pilot does not meet any of the section 61.51(e)(4) circumstances.
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2009 Murphy Interpretation (one of a number of questions in the letter)
So, yes, a student pilot may log PIC during the practical test (I never even suggested they could not) but if you don't think this is mental gymnastics using an analysis akin to the infamous
Beane letter (an unverified Chief Counsel interpretation allowing the only rated pilot on board to log PIC despite not fitting into 61.51), I guess we just have to disagree on the definition of "mental gymnastics."