Solution

Black Box Boundary Value Analysis (BVA)

Concept: Errors cluster at boundaries. Instead of random values, test at edges of equivalence partitions. For a range $[min, max]$, test: $min, min+1, max-1, max, min-1, max+1$ (invalid).

How boundary conditions tested:

1. Identify input domain boundaries from SRS (e.g., age 18-60, array size 1-100)
2. Create equivalence partitions (valid / invalid)
3. Pick values: at boundary, just inside, just outside
4. For $n$ variables, $4n+1$ test cases (or $6n+1$ with invalid). Also robust BVA includes invalid.

Example: Program accepts marks 0-100, grade calculation.

Test Case	Input	Expected
Below lower	-1	Invalid
At lower	0	Pass (F)
Just above lower	1	Pass
Mid	50	Pass
Just below upper	99	Pass
At upper	100	Pass (A)
Above upper	101	Invalid

Boundary coverage: Detects off-by-one errors like if (marks > 0 && marks < 100) incorrectly rejecting 0/100.

Advantage: Minimum test cases, maximum fault detection at edges where developers often use < vs <= incorrectly.