If you use the word "rate", most native english speakers are going to give you their opinion, not the outcome of a series of tests. This is the way i set it up when i have an app in testing and am requesting user testers:
The real problem, however, is that there is any need to plug (advertise) testing in the first place. Users eager to download an app can not be expected to do a good job testing it. The ones you can count on to be more impartial are those "weird" (not my word) blessed souls who go through the testing queue because they want to contribute in that way. I wouldn't mention the testing at all in a thread if i thought ten "real" tests was necessary, so i guess my opinion was revealed when i started asking for testers. The way to solve this is either to reduce the total karma so no need is felt to appeal to users to test, or to add a separate requirement for "official testers" so that we can be sure the app is given a thorough test. The first option would be acceptable to me, but the latter (which will require more work on the infrastructure, yes) is the best because it lets the dev sollicit user testing without making them jump through hoops--and this is the process most likely to get him feedback on usabiity issues.

Here's what happens in the rare case that one of the solicited user testers tries to jump through the requested hoops rather than just going and giving a thumbs up:
And then later:
The current system is too much of one, too little of another.