Boundary case

The term boundary case is frequently used in software engineering to refer to the 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, entering the values -1, 0, 100, and 101 would represent the boundary cases.

It is commonly thought that three cases should be used when boundary testing (one on the boundary, and one either side to it), the case on the valid side of the boundary is actually redundant, and will be picked up by other valid Equivalence partitioning. Thus only two cases should be used for each bounday, on the boundary and just past it.

A more full article on black box test techniques is to be found on the Boundary Value Analysis page.

See also corner case and edge case.