Boundary case

In software engineering, a boundary case is a behavior of a system when one of its inputs is at or just beyond its maximum or minimum limits. It is frequently used when discussing software testing.

For example, if an input field is meant to accept only integer values 0–100, then examples of boundary cases would be entering the values -1, 0, 100, and 101. A common technique for testing boundary cases is to perform three tests: one on the boundary and one on either side of it. For the previous example, this would involve testing -1, 0, 1, 99, 100, and 101.