Software Testing - Boundary-value analysis

Boundary-value analysis is a variant and refinement of equivalence partitioning, with two major differences: First, rather than selecting any element in an equivalence class as being representative, elements are selected such that each edge of the EC is the subject of a test. Boundaries are always a good place to look for defects. Second, rather than focusing exclusively on input conditions, output conditions are also explored by defining output ECs. What can be output? What are the classes of output? What should I create as an input to force a useful set of classes that represent the outputs that ought to be produced? The guidelines for boundary-value analysis are: · If an input specifies a range of valid values, write test cases for the ends of the range and invalid-input test cases for conditions just beyond the ends. Example: If the input requires a real number in the range 0.0 to 90.0 degrees, then write test cases for 0.0, 90.0, -0.001, and 90.001. · If an input specifies a number of valid values, write test cases for the minimum and maximum number of values and one beneath and beyond these values. Example: If the input requires the titles of at least 3, but no more than 8, books, then write test cases for 2, 3, 8, and 9 books. · Use the above guidelines for each output condition. Boundary-value analysis is not as simple as it sounds, because boundary conditions may be subtle and difficult to identify. The method does not test combinations of input conditions.