An interactive debugger is an outstanding example of what is not needed - it encourages trial-and-error hacking rather than systematic design, and also hides marginal people barely qualified for precision programming.
The only way for errors to occur in a program is by being put there by the author. No other mechanisms are known. Programs can't acquire bugs by sitting around with other buggy programs. Right practice aims at preventing insertion of errors and, failing that, removing them before testing or any other running of the program.