Boundary value analysis
A grading system accepts whole-number scores from 2 to 53 and rejects anything else.
Practice · Test design
Boundary value analysis questions and answers
Exam-style boundary value analysis questions, generated fresh each time, with answers computed to the ISTQB Foundation Level v4.0 definitions (section 4.2.2). Every wrong answer tells you which mistake leads to it.
No answers yet
What the syllabus asks for
Boundary value analysis tests the edges of ordered partitions: a partition's boundary values are its minimum and maximum. It rests on equivalence partitioning, so the partitions come first.
In 2-value BVA each boundary value has two coverage items: the boundary value itself and its closest neighbour in the adjacent partition. In 3-value BVA there are three: the boundary value and both of its neighbours. The syllabus notes that 3-value BVA is more rigorous, and it can find defects that 2-value BVA misses.
Worked examples
Example 1
A grading system takes a whole-number score, where 9 to 31 gets a pass. Scores below 9 or above 31 are rejected as invalid.
How many coverage items does 3-value boundary value analysis identify for the exam score?
- A. 4
- B. 8
- C. 12
- D. 6
Show the answer
Answer: 8. The boundary values are 8, 9, 31, 32. Each one and both of its neighbours, with duplicates counted once, gives 7, 8, 9, 10, 30, 31, 32, 33: 8 coverage items.
- 4: That is the 2-value count. 3-value BVA also includes each boundary value's neighbour inside its own partition.
- 12: That is three values per boundary value without removing duplicates. Neighbours overlap: the neighbour of one boundary value is often another boundary value.
- 6: That is three values per boundary. The v4.0 syllabus counts three per boundary value: each boundary value and both of its neighbours.
Try this one in the quiz: open example 1.
Example 2
A car insurer quotes online for drivers aged 16 to 23, in whole years. Anyone younger or older can't get a quote online.
Which set of values is exactly the 2-value boundary value analysis coverage items for the driver's age?
- A. 16, 23
- B. 15, 16, 17, 22, 23, 24
- C. 16, 17, 22, 23
- D. 15, 16, 23, 24
Show the answer
Answer: 15, 16, 23, 24. Accepted values run from 16 to 23, so the partitions are: below 16, 16–23, and above 23. The boundary values are the ends of each partition that has an end: 15, 16, 23 and 24.
- 16, 23: Those are only the valid boundary values. 2-value BVA also tests the closest neighbour across each boundary, in the invalid partitions.
- 15, 16, 17, 22, 23, 24: That is the 3-value set. It achieves 2-value coverage too, but it isn't exactly the 2-value coverage items.
- 16, 17, 22, 23: Those stay inside the valid partition. A boundary value's neighbour in 2-value BVA is the one across the boundary, in the adjacent partition.
Try this one in the quiz: open example 2.
Example 3
An online shop accepts orders of 3 to 19 items. Any other quantity is rejected.
Which set of values is exactly the 2-value boundary value analysis coverage items for the order quantity?
- A. 3, 19
- B. 3, 4, 18, 19
- C. 2, 3, 4, 18, 19, 20
- D. 2, 3, 19, 20
Show the answer
Answer: 2, 3, 19, 20. Accepted values run from 3 to 19, so the partitions are: below 3, 3–19, and above 19. The boundary values are the ends of each partition that has an end: 2, 3, 19 and 20.
- 3, 19: Those are only the valid boundary values. 2-value BVA also tests the closest neighbour across each boundary, in the invalid partitions.
- 3, 4, 18, 19: Those stay inside the valid partition. A boundary value's neighbour in 2-value BVA is the one across the boundary, in the adjacent partition.
- 2, 3, 4, 18, 19, 20: That is the 3-value set. It achieves 2-value coverage too, but it isn't exactly the 2-value coverage items.
Try this one in the quiz: open example 3.
What this is not
These are not questions from any ISTQB exam, and this site has no connection with ISTQB or any exam provider. Older question banks often use definitions from before version 4.0, so if an answer here disagrees with one you’ve seen elsewhere, check which syllabus it was written for. How the questions are made explains how every answer is checked.
To see the technique applied, read the four black-box techniques on one real checkout. To work your own example through, use the boundary value generator.