Types and Tests
<i>What about invalid arguments? What if someone calls: (random-elements -23 nil)? Should I write tests for those cases?</i><p><i>The function already handles negatives by returning an empty list for any count less than one. This isn’t tested; but the code is pretty clear. In the case of the nil, an exception will be thrown. That’s OK with me. This is a dynamically typed language. You get exceptions when you mess up the types.</i><p><i>Is that a risk? Sure, but only if some other part of the system was written without tests. If you call this function from a module that you wrote with tests, using something as effective as the TDD discipline, you won’t be passing nil or negative numbers, or any other form of invalid arguments. So I’m not going to worry about that. It’s on you.</i><p>This attitude coming from an experienced software developer is hard to fathom.  Sure, if you&#x27;re an experienced and meticulous developer that fully embraces TDD and you only work with other experienced and meticulous developers that full embrace TDD on the same type of software handling the same types of problems over and over, then sure, you might be able dodge a pretty high percentage of bugs a pretty high percentage of the time.<p>But most teams in the real world have a mix of inexperienced and experienced developers, meticulous and careless developers, developers that embrace TDD to varying degrees, and work on a variety of problems in a mix of domains with which the team members have varying degrees of experience.<p>So now your choices are:<p>1) code each and every function in a way that gives you high confidence that it works for the happy path and rely on the discipline of your team to ensure that no unhappy paths are hit<p>or, for approximately the same level of effort:<p>2) code each and every function in a way that gives you high confidence that it works for the happy path and which you have an extremely high degree of confidence that no unhappy paths even exist at all<p>It&#x27;s just not a tough decision for me.