Boundary Value Analysis

Learning objectives#

• Identify boundaries from requirements
• Choose boundary test values
• Apply BVA to lengths, dates and amounts
• Combine with equivalence partitioning

Explanation#

For a range min–max, test min-1, min, min+1, max-1, max and max+1 (the three-value approach). A two-value approach uses min-1, min, max, max+1.

Boundaries exist for numbers, string lengths, dates, file sizes, counts and money.

Off-by-one errors (> instead of >=) are among the most common defects.

Code example: Password length 8–20#

1Value (length)   Expected
27                Rejected: "Use 8–20 characters"
38                Accepted   ← min
49                Accepted
519               Accepted
620               Accepted   ← max
721               Rejected
8

9Bug found: length 20 rejected → code used "length < 20" instead of "length <= 20".

Six boundary tests reveal an off-by-one bug that typical “normal” values would never hit.

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. Read the min and max from the requirement.
2. Test just below, on and just above each edge.
3. Compare actual with expected.
4. Report off-by-one defects with the exact value.

Real-world use case#

Common mistakes#

Best practices#

• List every range in the requirements
• Test both sides of each boundary
• Include dates and lengths
• Report the exact failing value

Remember this#

Practice exercise#

14.99 MB (accept), 5.00 MB (accept), 5.01 MB (reject), 0 bytes (check behaviour)

Mini quiz#

Want more? Practise all Manual Testing MCQs · Manual Testing interview questions

Related topics#

My notes#

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