Why do edge cases and integration bugs still slip past our tests?
You and your team have gotten good at the obvious work. Known inputs, single functions, the paths you can picture. That part is solid now, and you should not pretend otherwise — it is a real gain. What gets past you lives in the space between things. One service assumes the data was already checked. Another assumes it wasn't. Nobody owns that gap, so nobody tests it. The failure is not in your code. It is in the handoff between your code and theirs. More test coverage will not fix this. What fixes it is naming the handoffs out loud, and giving someone the job of being suspicious of every assumption your teammates made about each other's work.
You test what you expect. Edge cases and integration failures live in what you did not expect — in the gap between two people's assumptions. Stop adding more tests to the parts you understand. Assign someone to hunt the seams between components, where no one owns the whole picture.
What changes unlock by starting
- Integration failures get caught before release more often than after.
- Your team names handoff points out loud instead of assuming someone else covered them.
- Fewer moments of 'I thought your part checked that.'
- A shared, growing list of past edge cases that becomes real institutional memory.