Boundary Value Analysis (BVA)
Boundary value analysis is a technique for test data selection. A test engineer chooses values that lie along data extremes. Boundary values include maximum, minimum, just inside boundaries, just outside boundaries, typical values, and error values. The expectation is that, if a systems works correctly for these extreme or special values, then it will work correctly for all values in between. An effective way to test code, is to exercise it at its natural boundaries.
E.g. if a text box is supposed to accept values in range 1 to 100, then try providing the following values:
1) 1, 100, values between 1 and 100 on sampling basis,
2) 0, 101,
3) Negative values,
4) Extremely large values