BOUNDARY VALUE TESTING
Introduction
Experience has shown that the boundaries of input and output ranges of a software component are common locations for errors that result in software faults. Boundary value analysis assists with the design of test cases that will exercise these boundaries in an attempt to uncover faults in the software during the testing process.
The expected input and output values should be extracted from the component specification. The input and output values to the software component are then grouped into sets with identifiable boundaries. Each set, or partition, contains values that are expected to be processed by the component in the same way. Partitioning of test data ranges is explained in the equivalence partitioning test case design technique. It is important to consider both valid and invalid partitions when designing test cases.
For an example where the input values were months of the year expressed as integers, the input parameter 'month' might have the following partitions:
... -2 -1 0 1 .............. 12 13 14 15 ..... ---------------|-----------------|--------------------- invalid partition 1 valid partition invalid partition 2The boundaries are the values on and around the beginning and end of a partition. If possible test cases should be created to generate inputs or outputs that will fall on and to either side of each boundary. This would result in three cases per boundary. The test cases on each side of a boundary should be in the smallest increment possible for the component under test. In the example above there are boundary values at 0,1,2 and 11,12,13. If the input values were defined as decimal datatype with 2 decimal places then the smallest increment would be the 0.01.
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.Boundary value analysis can be used throughout the testing cycle and is equally applicable at all testing phases.
After determining the necessary test cases with equivalence partitioning and subsequent boundary value analysis, it is necessary to define the combinations of the test cases when there are multiple inputs to a software component.