The automated tests are not panacea of course. Yet, you need to have enough tests to give you confidence that the change indeed is breaking nothing. It is one s

The automated tests are not panacea of course. Yet, you need to have enough tests to give you confidence that the change indeed is breaking nothing. It is one story to perform a deep refactoring on a C++ or Java code with 95% tests code coverage where either compiler or tests will pickup things for you. And it is a completely another story to do a refactoring on a PHP frontend code w/o any compiler/static analyzer and w/o any tests where your best tool is search-and-replace. Even the "depth" of safe refactoring will be very different in those two cases.