No. 26 “Edge cases?”

the weird stuff that’ll happen anyway.

An edge case is the rare stuff: the 35-letter name, the empty cart, the 9,999 notifications.

Rare for one person. With enough users, someone hits it every day.

Test with the longest real name you can find.

Engineers say edge case for a problem that only shows up at extremes: max volume, zero items, the longest name. Nobody owns the term.

In 2010, programmer Patrick McKenzie listed 40 falsehoods programmers believe about names. Long ones are just the start.

• Wikipedia, “Edge case” & “Corner case”
• Patrick McKenzie, “Falsehoods Programmers Believe About Names” (2010)

Save this for the next time every name in the mockup is “Jo.”