### What is a Boundary Value

A boundary value is any input or output value on the edge of an equivalence partition.

**Let us take an example to explain this:**

Suppose you have a software which accepts values between 1-1000, so the valid partition will be (1-1000), equivalence partitions will be like:

Invalid Partition | Valid Partition | Invalid Partition |
---|---|---|

0 | 1-1000 | 1001 and above |

And the boundary values will be 1, 1000 from valid partition and 0,1001 from invalid partitions.

**Boundary Value Analysis** is a black box test design technique where test case are designed by using boundary values, BVA is used in range checking.

**Example:2**

A store in city offers different discounts depending on the purchases made by the individual. In order to test the software that calculates the discounts, we can identify the ranges of purchase values that earn the different discounts. For example, if a purchase is in the range of $1 up to $50 has no discounts, a purchase over $50 and up to $200 has a 5% discount, and purchases of $201 and up to $500 have a 10% discounts, and purchases of $501 and above have a 15% discounts.

We can identify 4 valid equivalence partitions and 1 invalid partition as shown below.

Invalid Partition | Valid Partition(No Discounts) | Valid Partition(5%) | Valid Partition(10%) | Valid Partition(15%) |
---|---|---|---|---|

$0.01 | $1-$50 | $51-$200 | $201-$500 | $501-Above |

From this table we can identify the boundary values of each partition. We assume that two decimal digits are allowed.

Boundary values for Invalid partition: 0.00

Boundary values for valid partition(No Discounts): 1, 50

Boundary values for valid partition(5% Discount): 51, 200

Boundary values for valid partition(10% Discount): 201,500

Boundary values for valid partition(15% Discount): 501, Max allowed number in the software application