Ruby: Assign output of a function only if it does not return nil

When programming in Ruby I quite often have assignments like the following

test = some_function if some_function

With that assignments I want to assign the output of a function, but if it returns nil I want to keep the content of the variable. I know there are conditional assignments, but neither ||= nor &&= can be used here. The shortest way I found to describe the statement above is

test = (some_function or test)

Is there a better / shorter way to do this?