As a member of the CF, if you believe you might be pregnant (as was already mentioned), you must report it. To randomly test everyone for pregnancy, whether or not there is just cause is as ridiculous as randomly testing all members for diabetes, epilepsy, or cancer even with no indication of the illness. Yes, there is a minute possibility of having the illness and not being aware of it, but does that justify the test? Hardly. Just because you're female doesn't mean you're automatically pregnant every time you're sick, or that you're so irresponsible that you wouldn't report it if you suspected it.
If all men were subjected to a test for prostate cancer (and I think we ALL know what that test involves...), just in the off chance that someone might have it and not report it, because it could adversely effect their ability to do their job, there would be an uproar. I think most people are more than capable of looking after their own health, and are responsible enough to report a problem that would interfere with their work. Besides, if they knew and didn't report it, they could be charged.
Again, how would a pregnancy test be relevant on a recruiting test? Would it not be just as discriminatory to deny employment to a pregnant women as it would be for a father of young children? By the time she made it in, the kid would have been born already.