Boundary Value Analysis Test case design technique is one of the testing techniques. You could find other testing techniques such as Equivalence Partitioning, Decision Table and State Transition Techniques by clicking on appropriate links.
Boundary value analysis (BVA) is based on testing the boundary values of valid and invalid partitions. The Behavior at the edge of each equivalence partition is more likely to be incorrect than the behavior within the partition, so boundaries are an area where testing is likely to yield defects.
Every partition has its maximum and minimum values and these maximum and minimum values are the boundary values of a partition.
A boundary value for a valid partition is a valid boundary value. Similarly a boundary value for 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 test for each boundary value is chosen.
For each boundary, we test +/-1 in the least significant digit of either side of the boundary.
Boundary value analysis can be applied at all test levels.
Example on Boundary Value Analysis Test Case Design Technique:
Assume, we have to test a field which accepts Age 18 – 56
Minimum boundary value is 18
Maximum boundary value is 56
Valid Inputs: 18,19,55,56
Invalid Inputs: 17 and 57
Test case 1: Enter the value 17 (18-1) = Invalid
Test case 2: Enter the value 18 = Valid
Test case 3: Enter the value 19 (18+1) = Valid
Test case 4: Enter the value 55 (56-1) = Valid
Test case 5: Enter the value 56 = Valid
Test case 6: Enter the value 57 (56+1) =Invalid
Assume we have to test a text field (Name) which accepts the length between 6-12 characters.
Minimum boundary value is 6
Maximum boundary value is 12
Valid text length is 6, 7, 11, 12
Invalid text length is 5, 13
Test case 1: Text length of 5 (min-1) = Invalid
Test case 2: Text length of exactly 6 (min) = Valid
Test case 3: Text length of 7 (min+1) = Valid
Test case 4: Text length of 11 (max-1) = Valid
Test case 5: Text length of exactly 12 (max) = Valid
Test case 6: Text length of 13 (max+1) = Invalid