Edge case
An unusual situation at the limits of normal use, like an empty list, a very long name, or two people editing at once.
Normal case
- One person books
- Name is "Ana Ruiz"
- Clicks once
Edge cases
- Two book the same slot
- 80-character name
- Double-click on Book
What it is
An edge case is a situation that doesn't happen often but breaks things when it does: a name with 80 characters, an order of zero items, a date on February 29, a user who double-clicks Submit, someone losing connection mid-upload.
Builders naturally focus on the normal case. Listing the edge cases you care about up front ("what happens if…?") prevents a lot of bugs.
You don't need to cover every possibility. Pick the ones that would actually hurt your users.
How to ask for it
“Make sure it works properly.”
“Handle these edge cases in the booking form: two customers booking the same slot at the same moment (second one gets "slot just taken"), double-clicking Book (only one booking), and names over 60 characters (truncate with ellipsis in the schedule).”
"Works properly" assumes the builder will imagine the same problems you do; listing edge cases makes them explicit.
You've seen this in
- VLayouts breaking on very long product names
- DDouble charges from double-clicking Pay
- CCalendar bugs around daylight saving time