Boundary Value Analysis (BVA)
Testing at the edges of equivalence partitions, where bugs are most likely to occur.
Full definition
Boundary Value Analysis (BVA) is a test design technique that focuses on testing at the boundaries of equivalence partitions. Experience shows that bugs cluster at boundaries — the exact point where valid input becomes invalid.
For a field accepting values 1-100:
- Boundaries to test: 0, 1, 2, 99, 100, 101
- The values just below, at, and just above each boundary
Two-value BVA (standard):
- Test the boundary value and the value just outside
- For range 1-100: test 0, 1, 100, 101
Three-value BVA (robust):
- Test the value just below, at, and just above each boundary
- For range 1-100: test 0, 1, 2, 99, 100, 101
BVA is one of the most effective testing techniques — it catches the classic 'off-by-one' errors that are among the most common programming mistakes.
Always combine BVA with Equivalence Partitioning for comprehensive black-box test design.
Interview tip
Classic interview question: 'Design test cases for a field accepting ages 18-65.' Apply both EP and BVA to give a thorough answer.