TDD: why might it be wrong to let app code know it is being tested, not run?

Question

In this thread, Brian (the only answerer) says \"Your code should be written in such a fashion that it is testing-agnostic\"

The single comment says \"Your code shou

Answer 1

Think of the big Volkswagen scandal. A system which behaves differently under test than under production load isn't really tested. That is: it is really two systems, the production system and the test system - and the only one of these which is tested is the test system. The production system, being different, is not tested. Every difference in behavior you introduce between the two systems is a testing vulnerability.