But the practice tests are just that - practice. They're not real, actual tests with real, actual questions - they're put out by companies trying to "simulate" the real thing.
Use them as a guide to see if you're improving - that's it.
It's like any other test you've taken out there. You don't take a practice bio test to predict how you're going to do on the final (e.g. an 85% on the practice test doesn't equate to an 85% on the final). You can, however, use more than one test to see if you're improving or getting worse.
I've just seen too many people get burned because they were consistently scoring in the low 30s - and hence they thought they were going to score similarly on the real test - when what they should have focused on is the fact that their practice scores were variable and often didn't show much improvement at all.
Just be cautious, is all I'm saying.