August 26, 2010

Boundary Value Analysis

Boundary Value Analysis

Boundary Value Analysis (BVA) is a test data selection technique (Functional Testing technique) where the extreme values are chosen. Boundary values include maximum, minimum, just inside/outside boundaries, typical values, and error values. The hope is that, if a system works correctly for these special values then it will work correctly for all values in between.
§ Extends equivalence partitioning
§ Test both sides of each boundary
§ Look at output boundaries for test cases too
§ Test min, min-1, max, max+1, typical values
§ BVA focuses on the boundary of the input space to identify test cases
§ Rational is that errors tend to occur near the extreme values of an input variable
There are two ways to generalize the BVA techniques:
1. By the number of variables
o For n variables: BVA yields 4n + 1 test cases.
2. By the kinds of ranges
o Generalizing ranges depends on the nature or type of variables
§ NextDate has a variable Month and the range could be defined as {Jan, Feb, …Dec}
§ Min = Jan, Min +1 = Feb, etc.
§ Triangle had a declared range of {1, 20,000}
§ Boolean variables have extreme values True and False but there is no clear choice for the remaining three values
Advantages of Boundary Value Analysis

  • Robustness Testing - Boundary Value Analysis plus values that go beyond the limits

  • Min - 1, Min, Min +1, Nom, Max -1, Max, Max +1

  • Forces attention to exception handling

  • For strongly typed languages robust testing results in run-time errors that abort normal execution
Limitations of Boundary Value Analysis
BVA works best when the program is a function of several independent variables that represent bounded physical quantities
1. Independent Variables

  • NextDate test cases derived from BVA would be inadequate: focusing on the boundary would not leave emphasis on February or leap years

  • Dependencies exist with NextDate's Day, Month and Year

  • Test cases derived without consideration of the function
2. Physical Quantities

  • An example of physical variables being tested, telephone numbers - what faults might be revealed by numbers of 000-0000, 000-0001, 555-5555, 999-9998, 999-9999?

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