# 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.

```csharp
[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](https://www.ask-codey.com/glossary?category=unit-testing&level=2)

Updated: October 28, 2026

Source: https://www.ask-codey.com/glossary/edge-case