Edge Case

noun

say it: “EJ kays” /ɛdʒ keɪs/

A test value at a limit or just past it, where bugs most often hide.

What is Edge Case?

Edge Case — A test value right at a limit or just past it: zero items, the very last day, or the 5th and the 6th book when a member may borrow 5. Bugs gather at edges, so good tests check both sides of every limit.

[TestMethod]
[DataRow(5, true)]   // exactly at the limit
[DataRow(6, false)]  // one past it
public void CanBorrow_AtTheLimit(int books, bool expected) =>
    Assert.AreEqual(expected, Library.CanBorrow(books));

In a sentence

• “We added an edge case test for the sixth book, one past the borrowing limit.”

Level: Apprentice · More Unit Testing terms at this level

Updated October 28, 2026