The final test is always human review. The point of testing is to simplify the analysis of correctness for humans.

Also, ideally your code and test are somewhat independently written, whether it is whitebox or blackbox. If that is the case,you greatly reduce the chance that both the code and the test are wrong in such a way that the test still passes.

This is why writing unit tests for stuff like getters and setters is really dumb. It doesn't really simplify checking whether the code is correct unless you use something like meanbean and thus provides some degree of separation between the test and the implementation.

Mutation testing is a way to test your tests.

And will very quickly humble even the most diligent of testers :) For example, you're testing that this value is in a range - but are you testing both endpoints and whether they're inclusive or exclusive? In faster languages I enjoy quickcheck style testing which also reveals these things pretty quickly.

Do not confuse end-to-end functional tests that this article is describing for smaller “unit” tests that you typically might express in quick check/mutation testing (at least as I understand the space).

tests of test tests are test tests, so just use your test testing tests to test your test tests

Somehow you build a feedback loop of tests.