> In a way, using tests to check code is like designing two trucks and having them pull against each other; if nothing breaks, you know they both work. ('bad m

> In a way, using tests to check code is like designing two trucks and having them pull against each other; if nothing breaks, you know they both work. ('bad metaphorical thinking' Dijkstra alert) This is wrong. If the tests pass, it is entirely possible that both the original code and the tests are faulty.