"It depends" is the only valid truism. There's no panacea for techniques, tools or philosophy. Fast-running TDD unit and smoke tests are great for non-fragile

"It depends" is the only valid truism. There's no panacea for techniques, tools or philosophy. Fast-running TDD unit and smoke tests are great for non-fragile, fast development, however throwing a "pry" or equivalent breakpoint in some code not behaving as expected can be immensely helpful. Heck, when I started out 25 years ago, trial-and-error in an IDE is how I learned how Turbo Pascal worked. REPLs and IDEs are great for digging into how a piece of code works live, while automated testing is to assure things aren't broken and code isn't treated as a sacred text.