Boundary Value Analysis
Also known as: BVA
Boundary value analysis is a test design technique that targets the edges of an input range — the minimum, maximum, and the values just inside and just outside them — because that's where off-by-one errors and validation bugs cluster. If a field accepts ages 18-65, BVA tests 17, 18, 65, and 66, not just a "normal" value like 30.
Most bugs in input validation don't happen in the comfortable middle of a range — they happen exactly at the edges, where a developer wrote <= instead of <, or forgot the range was inclusive on one side but not the other. Boundary value analysis exists because testing "a normal value and hoping for the best" almost never catches those.
For any bounded input, BVA tests four to six values: the minimum, one below the minimum, the maximum, one above the maximum, and often the minimum/maximum themselves plus one step inside. For a field accepting 1-100, that's 0, 1, 2, 99, 100, 101.
BVA pairs naturally with equivalence partitioning — partitioning tells you which classes of input exist (valid range, too low, too high), and boundary value analysis tells you exactly which values inside those classes are worth actually testing, instead of testing every possible value in a range that behaves identically.
Example
Field: "Quantity" accepts 1-10 items per order.
Test values: 0 (below min), 1 (min), 2 (min+1), 9 (max-1), 10 (max), 11 (above max)Six test values cover a ten-value range more effectively than testing all ten.
