Boundary Value Analysis — Standard Limits

If Equivalence Partitioning tells you which groups to test, Boundary Value Analysis tells you exactly where in those groups to look.

The boundary is where behavior changes. It's where "valid" becomes "invalid," where the discount triggers, where the system decides to accept or reject. And it's precisely where most bugs live.

Why Boundaries Break Things

Developers write code like this: if (age >= 18 && age <= 70). It looks simple. But there are four critical points: 17, 18, 70, 71. One off-by-one error in the condition (> instead of >=) and the 18-year-old is rejected — a bug that passes most tests and only surfaces at the exact boundary.

What You'll Learn

• The difference between two-point BVA (just inside/outside) and three-point BVA (just below/at/just above)
• How to identify physical boundaries vs. business-rule boundaries
• How to build a concise boundary test suite that catches off-by-one errors

Your Practice Challenge

The Age Validator enforces a 18–70 age range for driver's licenses. Your mission: test the exact boundary points — 17, 18, 19, and 69, 70, 71 — and observe whether the system handles each boundary correctly.

Six test cases. Maximum impact.