Guinea pig

A simile for a person, animal or thing used as a subject for experiment. e.g. "Who wants to be the guinea pig?" "He's going to be the guinea pig"
Why it matters
This language may not be inclusive of vegan colleagues as it references experimentation on non-human animals. Veganism is recognised as a philosophical belief and is protected by the Equality Act 2010.
Instead try saying:
Test case
Test subject
Volunteer