Boundary value analysis

Boundary value analysis (BVA) is based on testing at the boundaries between partitions. Note that we have both valid boundaries (in the valid partitions) and invalid boundaries (in the invalid partitions).

To apply boundary value analysis, we will take the minimum and maximum (boundary) values from the valid partition (1 and 99 in this case) together with.

• Ex: consider a printer that has an input option of the number of copies to be made, from 1 to 99.

The first or last value respectively in each of the invalid partitions adjacent to the valid partition (0 and 100 in this case). In this example we would have three equivalence partitioning tests (one from each of the three partitions) and four boundary value tests.

Open boundaries are more difficult to test, but there are ways to approach them. Actually the best solution to the problem is to find out what the boundary should be specified as!

One approach is to go back to the specification to see if a maximum has been stated somewhere else for a balance amount. If so, then we know what our boundary value is. Another approach might be to investigate other related areas of the system.

Extending equivalence partitioning and boundary value analysis So far, by using EP and BVA we have identified conditions that could be tested, i.e. partitions and boundary values

With boundary value analysis, we think of the boundary as a dividing line between two things. Hence we have a value on each side of the boundary (but the boundary itself is not a value).

                 Invalid                    Valid                           Invalid

                         0  | 1                                 99 |   1OO

Looking at the values for our printer example, 0 is in an invalid partition, 1 and 99 are in the valid partition and 100 is in the other invalid partition. So the boundary is between the values of 0 and 1, and between the values of 99 and 100. 

There is a school of thought that regards an actual value as a boundary value. By tradition, these are the values in the valid partition (i.e. the values specified). This approach then requires three values for every boundary two, so you would have 0,1 and 2 for the left boundary, and 98, 99 and 100 for the right boundary in this example. 

The boundary values are said to be 'on and either side of the boundary' and the value that is 'on' the boundary is generally taken to be in the valid partition.