Is it possible to write a unit test under a void function?

Question

C++ / C#

When writing a program in C++, I used void functions all the time.

Is it possible to test them in this case, and if so, how?
I was just reading about unit tests on the Internet, but everywhere people used int or double, and it became interesting whether it was possible to write under void.

Answer 1

If the function does not return anything, then it either changes the values ​​of its arguments passed by reference (pointer) or global variables, or outputs something to the console/window/port/socket/etc, otherwise it is useless.
Check any output that the function generates.