I can change if you'd prefer, but it seems that assign is what we want here.  My understanding of the difference is that with `assign` and `defaults`:

* `assign` -- the `source` (`{verbose:false}` in this case) will "win" (even if `options` already has a `verbose` property).
* `defaults` -- the `source` (`{{verbose:false}` in this case) will lose if `options` already has a `verbose` property.

It is a moot point in our case since we are creating `options` directly above and we know it cannot have a `verbose` prop in it, but if it were possible for `options` to have `verbose` already set I still think `assign` is the right call here since we **always** want `verbose` to be false when running under `testem` (the `testem` UI completely covers any logging anyways).