[posterboy]

It's a fact that you can't ever have enough tests, because, for one, the tests are not tested.

[Smurfix]

Of course the tests are tested – by the code they're covering, which is also covered by other tests.

[eru]

That's funny in practice. But does not have to be a problem in principle.

There are ways to test your tests (in a way that does not lead to an infinite regress), and alternatively you can also prove your tests correct; or just use plain old code review.