When Luck Is Enough🍀
Imagine the situation. You are hours into the process of creating a new and tricky feature. You’re feeling that coding pain you’ve felt dozens of times before, going through the painful process to craft great code with added panic as the deadline approaches.
You code a simple happy path solution. But today is that once in a while when a miracle happens. The type of thing that puts your faith back into yourself and the software development process. You add a unit test for a particular edge case you hadn’t previously considered, and your code just works™.
You’re probably a genius, or something.
When Your Code Handles an Unexpected Edge Case on Its Own
Because of course, we take full credit when this miracle happens, as if we had the foresight of a clairvoyant software architect.
“Ah yes, I totally anticipated that scenario”
You didn’t. You played your luck. Still, it’s one of those rare moments in development that feels like an undeserved win, like finding money in a coat pocket you forgot about (boomer example, I know).
The Nature of Edge Cases
Edge cases are the silent assassins of software stability.
They creep up in the weirdest ways and here is a greatest hits collection of my favorites from over the years:
a user entering a negative age (maybe we should handle that, said our product manager)
a leap year (how often are they again)
an API returning an empty response instead of an error (well done for planning the solution so well, team)
a front end developer whose “reusable screen” only works the very first time you view it. The second time it doesn’t work correctly (that’s barely even an edge case).
The best developers anticipate these, writing robust, defensive code to handle even the most ludicrous scenarios. But let’s be honest, there’s always something we miss and there will always be something we will miss.
So that’s why it’s so satisfying when, by some stroke of good design (or more likely sheer luck), your program just deals with it. Maybe a validation rule you added as an afterthought prevented an impossible state, or a function designed to be flexible just so happened to cover a weird edge case.
Whatever the reason, it feels like the coding gods (hello John Carmack) have smiled upon you.
When Luck Isn’t Enough
As much as we enjoy these unexpected victories, relying on luck isn’t exactly a scalable software development strategy. Edge cases are best dealt with through a series of tips, tricks and time-honored good practice.
Defensive programming
Assume everything that can go wrong will go wrong.
Thorough testing
Unit tests, integration tests, and even chaos engineering can help uncover hidden pitfalls and pratfalls.
User feedback
No matter how well we plan, real-world users will always find new and creative ways to break our applications.
Conclusion
Let us Celebrate, Then Investigate
So, when your code magically handles an edge case, take a moment to celebrate — but then, take another moment to understand why it worked. Did you accidentally write something brilliantly resilient? Or did you simply get lucky? If it’s the latter, it’s worth reinforcing that success with deliberate design, ensuring the next unexpected scenario doesn’t end in disaster.
Because for every moment when your program unexpectedly works, there’s another where it will absolutely, spectacularly fail. And those are the moments we prefer to avoid.