It was one of those Friday afternoons that every software team knows well—the kind where you can almost taste the weekend. The sprint was winding down, and conversations in the office (and Slack) were drifting toward movie plans, weekend trips, and much-needed rest. —the
We’d had a productive wee optimization—nothing. One of our developers, confident in a recent tweak to a core backend service, decided to push a small update before heading out. It was meant to be a quick performance optimization—nothing that looked risky on the surface.
The commit went through. Our Continuous Integration (CI) pipeline fired up as usual, running the automated checks we had in place.
And then, the screen lit up red.
The Unexpected Failure
One unit test had failed. Just one.
Our first thought? “Probably a flaky test. Let’s just rerun it.”
We’d seen that happen before—some tests would occasionally fail for environmental reasons rather than actual code problems.
But this time was different. Rerunning the pipeline didn’t help. The same test failed again, with the exact same result.
When we dug in, the problem became clear: the code change had subtly altered the behavior of a critical function that multiple services depended on. It wasn’t an obvious bug—no glaring syntax errors, no crashes—but in certain cases, the output would be wrong.
If this had gone live, we wouldn’t have discovered it until a customer reported an issue. Given how central this function was, it might have caused disruptions across several parts of our product. And since it was Friday evening, we probably wouldn’t have heard about it until Saturday or Sunday. That would have meant engineers on emergency calls, hurried hotfixes, and a weekend lost to firefighting.
Instead, that single unit test stopped the bad code in its tracks.
The Quick Recovery
Once we identified the failing logic, the fix was straightforward. The developer rolled back the problematic change, corrected the function, and pushed a new update. This time, the pipeline passed with a reassuring wall of green checkmarks.
Within an hour, the crisis had been resolved—before it even had a chance to reach production. The weekend was safe. Customers remained blissfully unaware.
It was such a small thing on the surface, but it felt like a huge win.
The Real Value of Unit Tests
Unit tests often don’t get the credit they deserve. They sit quietly in the background, running after every commit, catching issues that might otherwise slip through.
Think of them as safety nets for software teams:
- Early Detection – They catch problems long before code reaches production.
- Confidence for Developers – With solid test coverage, developers feel safer refactoring, experimenting, or deploying quickly.
- Faster Deployment Cycles – Automated checks reduce the need for extensive manual testing.
- Protection Against Regressions – Future updates are less likely to accidentally break existing features.
- Team Morale – Fewer production issues mean less stress, fewer late-night fixes, and more trust in the codebase.
They might not be flashy, but their impact is huge.
Lessons Learned from That Friday
That day taught us something important: unit tests don’t just improve code quality — they protect people.
They protect:
- Customer Experience – By catching bugs before they cause frustration.
- Team Productivity – By preventing time from being wasted on emergency fixes.
- Company Reputation – By reducing the risk of public service interruptions.
- Work-Life Balance – By allowing engineers to actually enjoy their weekends.
It also reinforced another truth: skipping tests for “just a small change” is risky. Bugs don’t care about the size of your commit — they care about whether they can sneak through unnoticed.
Building a Culture of Testing
The best safeguard against production disasters isn’t luck—it’s a consistent testing culture. This means:
- Writing tests for all core logic—especially the parts of the system that everything else depends on.
- Making Testing Part of the Workflow—Treating failing tests as serious blockers, not minor inconveniences.
- Encouraging Developers to Think About Edge Cases – Bugs often live in the scenarios no one thought to check.
- Keeping Tests Fast—So they run frequently without slowing down development.
When testing becomes second nature, you’re not just writing code—you’re building confidence.
The Moral of the Story
That Friday afternoon could have ended very differently. We could have spent our weekend patching a broken production environment. Instead, one well-written unit test gave us a safety net.
It was a reminder that good tests are like insurance policies: you don’t appreciate them every day, but when you need them, they’re invaluable.So, the next time you wonder if a unit test is worth writing, remember this:
the smallest test might one day save your biggest weekend.