Think about how much time you will spend if a customer reports a new bug. First, you spend time trying to reproduce the bug. Next, you have to debug and fix the problem. Finally, you have to write single class tests. In general, reproducing the bug alone will cost more time than you spent debugging a feature test. In fact, if you have trouble debugging a properly-designed feature test, it is actually the same as debugging your whole server and we assert you have bigger issues if you have trouble debugging your server.