test: fix default value for additional param

In Python, the default values of parameters are evaluated only once
during their declaration. So, whenever the default parameter is used
the same object will be used. Since we use a list, which is a mutable
object, this could lead to unexpected results.

PR-URL: https://github.com/nodejs/node/pull/2553


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>