Yesterday I tried covering an important topic of ISTQB which is Boundary value analysis.

Typically Boundary value analysis is a software testing technique to determine test cases covering known areas of frequent problems at the boundaries of software component input ranges

You’ll also need to know Equivalence partitioning before understanding it.

Inputs to the software or system are divided into groups that are expected to exhibit similar behavior,
so they are likely to be processed in the same way. Equivalence partitions (or classes) can be found
for both valid data and invalid data, i.e. values that should be rejected. Partitions can also be identified
for outputs, internal values, time-related values (e.g. before or after an event) and for interface
parameters (e.g. during integration testing). Tests can be designed to cover partitions. Equivalence partitioning (EP) is applicable at all levels of testing.
Equivalence partitioning as a technique can be used to achieve input and output coverage. It can be applied to human input, input via interfaces to a system, or interface parameters in integration testing.

So as of now behavior at the edge of each equivalence partition is more likely to be incorrect, so boundaries are an
area where testing is likely to yield defects. The maximum and minimum values of a partition are its
boundary values. A boundary value for a valid partition is a valid boundary value; the boundary of an
invalid partition is an invalid boundary value. Tests can be designed to cover both valid and invalid
boundary values. When designing test cases, a value on each boundary is chosen.
Boundary value analysis can be applied at all test levels. It is relatively easy to apply and its defect finding capability is high; This technique is often considered an extension of equivalence partitioning and can be used on input by humans as well as,for example, on timing or table boundaries. Boundary values may also be used
for test data selection.

Some questions that have been asked for these concepts are:

Order numbers on a stock control system can range between 10000 and 99999 inclusive. Which of the following inputs might be a result of designing tests for only valid equivalence classes and valid boundaries?

a) 1000, 50000, 99999

b) 9999, 50000, 100000

c) 10000, 50000, 99999

d) 10000, 99999, 100000

An input field takes the year of birth between 1900 and 2004

The boundary values for testing this field are

a. 0,1900,2004,2005

b. 1900, 2004

c. 1899,1900,2004,2005

d. 1899, 1900, 1901,2003,2004,2005

I hope u’ll find this useful.