Hi, and welcome!
Please see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers. This one, however, doesn't quite need it.
The add_row line dutifully returns a value, but it is ephemeral because it wasn't assigned to a name that would preserve it.
Try
add_row(test, x = 0, y = 1, z = 2) -> test