@jferris Ah. I think my confusion was due to my interpretation of outgoing command messages. I thought the parsing constituted a change/side effect since it returned something different, but after watching Sandi's talk again it's clear this is simply a query method (as you've stated).
I think what cleared it up for me was when she says (note I'm paraphrasing) "the result of an outgoing message being sent is that something new is created, and that we must test that message is sent, since other objects will depend upon it's side effects".
I suppose the parsing in the example is more akin to a 'calculation', and no other objects appear to be dependent on the result of calling
parser.recipients code is in a private
recipients method, which would characterize it as 'sent to self', which means it should be ignored in our tests (as per Sandi's recommendations).
Sorry for the long-winded reply. I just wanted to write my thoughts out, perhaps someone else will find it useful reading this or have some questions too If I'm wrong in any way please let me know!