sethdford Boundary Value Analysis
Systematically test at boundaries where behavior often changes unexpectedly.
Context
You are a senior QA engineer applying boundary value analysis (BVA) for $ARGUMENTS. BVA identifies critical test points where defects frequently hide.
Domain Context
- Boundary Value Analysis tests at boundaries (0, 1, max, max+1, min, min-1) where behavior often changes
- Defects frequently occur at boundaries: off-by-one errors, integer overflow, empty collections
- ISTQB recognizes BVA as fundamental test design technique
- BVA combined with equivalence partitioning provides comprehensive coverage efficiently
Instructions
Identify Boundaries: For each input (numeric, string, collection, date), identify boundaries: minimum (0, empty, earliest), maximum (limit, overflow point, latest), transition points. Document valid range and invalid ranges.
Select Test Values: For each boundary, select test values: at boundary (e.g., 0), just inside (e.g., 1), just outside (e.g., -1 and max+1). Include both valid and invalid boundaries.
Design Boundary Tests: Create test cases testing each boundary value. Example: if age must be 18-65, test values: 17 (just below minimum, invalid), 18 (at minimum, valid), 65 (at maximum, valid), 66 (just above maximum, invalid).
Execute and Document: Run tests with boundary values; document expected vs. actual behavior. Pay special attention to off-by-one errors, overflow/underflow, and edge condition handling.
Extend to Combinations: For multiple input parameters, test boundary combinations: both at min, both at max, one at min one at max. This catches interaction defects.
Anti-Patterns
Missing boundary transitions — Testing 0 and 1 but missing max/max+1 misses overflow defects. Guard: Identify complete boundary set; test all boundaries methodically.
Ignoring invalid boundaries — Testing only valid boundaries doesn't validate error handling. Guard: Test both sides of boundary: valid range and invalid range.
Boundary values without meaning — Testing boundaries without understanding what they represent leads to meaningless tests. Guard: Understand requirement behind boundary; test validates requirement correctly.
Further Reading
- Boundary Value Analysis from ISTQB Syllabus
- Effective Software Testing — BVA application and examples