I'm far from an expert, but the impression I get from our dojo is that the tests are more demonstrations than tests, and therefore unless something goes horribly wrong, everyone passes.
The senseis won't let people test who they aren't sure are ready and thus the real "test" is in whether or not your sensei thinks you are ready to represent the dojo at the test.
I agree until it is time to test for dan rank. I've seen many fail the shodan test. Some teachers look for certain things and if not seen they will fail you!