Kai, I strongly disagree.
Testing only proves that the circuit with those particular components work under those conditions that day. The only way to make a reliable thing is by design. I know that it is a pain in the gluteus maximus to calculate reliability rather than throwing the thang together and see it work, but no testing - unless extremely elaborate - takes component tolerances into account. Just look at the tolerance for ViL and ViH for the chip you would use for your oscillator and weep.

Erik