towards a contained test suite with no system state side effects

Here is a quick snapshot of my current work.
> 1. it can easily be used to apply options to all invocations of common.npm within a test

This makes sense.

2. by including it even when there are no options to send it establishes the pattern to be used, as a placeholder.

In previous projects I've been a proponent of this kind of boilerplate, but npm has traditionally stuck to a terser style (due to that being @isaacs's preference / him having written the bulk of the code). That said, yes, these tests end up being written by many hands, and consistency is a virtue because it makes it easy for others to follow the pattern. You've convinced me!