Just be sure to be honest, don't worry about hurting someone's feelings. If the instructions aren't clear, or the measurements don't work, please say so. There are a couple of pretty famous people out there with terrible patterns, that testers just gave praise, for whatever reason - wanting to be friends with the designer? When I sent a pattern to a few friends for testing, only one gave me the honest feedback I needed - a measurement was wrong - that made a big difference. I am so grateful that she caught it before it was published on my blog.