Never trust an engineer who says they don't need to write tests. It's somewhat of a dream for many engineers to be heads down working alone on deep technical problems but while coding may be solo endeavor, _code maintenance_ is a team sport. It's never good to let someone go it alone for too long.

Side note: It's much simpler to say "they/them" when referring to someone rather than "he/she", "s:he", and "his/her".