The transit of Mercury has been used in the past to demonstrate
a prediction of general relativity.
In fact an anomaly in the precession of Mercury troubled scientists
for many years before general relativity was able to account for it.
"Transits of Mercury and General Relativity from
observations, and the 2019 November 11 transit" two page
white paper :-
https://meetingorganizer.copernicus....2019-993-5.pdf