More than the act of testing, the act of designing tests is one of the best bug preventers known.
Extra features were once considered desirable. We now recognize that 'free' features are rarely free. Any increase in generality that does not contribute to reliability, modularity, maintainability, and robustness should be suspected.
A good threat is worth a thousand tests.
Testing proves a programmer’s failure. Debugging is the programmer’s vindication.
If you can't test it, don't build it. If you don't test it, rip it out.
First law: The pesticide paradox. Every method you use to prevent or find bugs leaves a residue of subtler bugs against which those methods are ineffective.