Can you tell me about the boundary value analysis technique?

Boundary Value Analysis (BVA) is a test design technique based on the assumption that errors often occur at the boundaries of input data or output results.

The principle of BVA involves testing values:

• At the very boundary of the permissible range.
• In close proximity to the boundary (left and right, or below and above).

For a range [min, max], values min, min+1, max-1, max are tested. Sometimes min-1 and max+1 are also included to check the handling of invalid values.

Example:

Input field for age, with an allowable range from 18 to 65 years.

Values tested by BVA:

• Valid: 18, 19, 64, 65
• Invalid (to check errors): 17, 66

This technique complements the Equivalence Partitioning technique. Data is first divided into equivalence classes, and then BVA is applied within each class (especially at the boundaries).

Advantages of BVA:

• High probability of finding errors related to comparison conditions (<, >, <=, >=).
• Systematic approach to selecting test data at boundaries.
• Reduces redundancy of tests compared to exhaustive testing.

Disadvantages of BVA:

• Not always applicable to non-numeric data (if clear "boundaries" are not defined).
• Does not detect errors unrelated to boundary conditions.