experimental subject

Urías had spent the previous five years as the Dodgers brain trust’s experimental subject, placed on innings limits and, once, a midseason break, all as part of a failed effort to protect his precocious left arm.

A member of Moon’s party fired back, arguing the head of state is not an experimental subject.

For the first few trials, the confederates reported accurately and the experimental subject of course agreed with them.

By the time the question came to the experimental subject, there was obvious psychic tension.

The one who was not "in on it" was the sole experimental subject, who was always placed at the last seat at the table.