Boundary-value analysis

The values could be input or output ranges of a software component, can also be the internal implementation.

Since these boundaries are common locations for errors that result in software faults they are frequently exercised in test cases.

It is important to consider both valid and invalid partitions when designing test cases.

When we compute the equalities:- we get back the values which are on the boundary, inclusive, that is these pairs of (a,b) are valid combinations, and no underflow or overflow would happen for them.

Boundary values (drawn only for the overflow case) are being shown as the orange line in the right hand side figure.

For another example, if the input values were months of the year, expressed as integers, the input parameter 'month' might have the following partitions: The boundary between two partitions is the place where the behavior of the application changes and is not a real number itself.

Where a boundary value falls within the invalid partition the test case is designed to ensure the software component handles the value in a controlled manner.