However beautiful the strategy, you should occasionally look at the results. — Sir Winston Churchill

As promised, firstly, the whys

As you probably know by now, Ruby is an interpreted language and along with
the upside of faster development cycle, there is a downside of not having a
compiler: there is no syntax or type checking after you write the
code. Executing the code is the only way to know if its valid and tests are a
great way to execute code.